#include <bits/stdc++.h>
using namespace std;
#include<ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;


#define ll long long
#define ull unsigned long long
#define ld long double
#define f(i,n) for(int i=0;i<n;i++)
#define pb push_back
#define YES cout<<"YES\n"
#define NO cout<<"NO\n"
#define endl '\n'
#define vll vector<ll>
#define mll map<ll,ll>
#define MOD 998244353
#define ANS cout<<ans<<endl
#define minHeap priority_queue<ll,vector<ll>,greater<ll>>
#define maxHeap priority_queue<ll>
#define fastio ios_base::sync_with_stdio(false);cin.tie(0); cout.tie(0);
typedef tree<ll,null_type,less<ll>,rb_tree_tag,tree_order_statistics_node_update>ordered_set;


ll gcd(ll a, ll b) {return __gcd(a,b);}
ll lcm(ll a, ll b) {return a* (b/gcd(a,b));}
//const int m=1e9+7;
long long binpow(long long a, long long b) {
    long long res = 1;
    while (b > 0) {
        if (b & 1)
        res = (res * a);
        a = (a * a);
        b >>= 1;
    }
    return res;
}
bool subseq(string a,string b)
{
    ll x=a.size();
    ll y=b.size();
    if(x>y)return 0;
    ll i = 0, j = 0;
    while (i < x && j < y ){
        if (a[i] == b[j])i++;
        j++;
    }
    return i==x;
}
bool iscomposite(ll n)
{
    for(int i=2;i<=sqrt(n);i++)
    {
        if(n%i==0)
        {
            return 1;
        }
    }
    return 0;
}

long long toDec(const string& binary) {
    long long decimal = 0;
    long long base = 1;
    for (int i = binary.size() - 1; i >= 0; --i) {
        if (binary[i] == '1') {
            decimal += base;
        }
        base *= 2LL;
    }
    return decimal;
}

string toBin(long long n) {
    string temp;
    if (n == 0) return "0";
    while (n > 0) {
        temp = (n % 2LL == 0 ? "0" : "1") + temp;
        n = n / 2LL;
    }
    return temp;
}

int calculateSum(const vector<int>& v) {
    int total = 0;
    for (int x : v) {
        total += x;
    }
    return total;
}

bool check(char c1, char c2){
    if (c1 == '(' && c2 == ')') return true;
    return false;
}


ll moduexp(ll a,ll b){
    ll ret=1;
    while(b){
        if(b%2)ret=(ret*a)%MOD;
        a=(a*a)%MOD;
        b/=2;
    }
    return ret;
}

ll moduinv(ll x) {
    return moduexp(x,MOD-2);
}

const int mx=6005;

ll parent[mx];

ll find(ll u) {
    if(parent[u]!=u)parent[u]=find(parent[u]);
    return parent[u];
}

bool uni(ll u, ll v) {
    ll pu=find(u);
    ll pv=find(v);
    if (pu==pv)return 0;
    parent[pu]=pv;
    return 1;
}
bool sortbyCond(const pair<int, int>& a, const pair<int, int>& b) {
    if (a.first != b.first)
        return a.first < b.first;
    else
        return a.second > b.second;
}

bool is_substring(string a, string b) {
    return b.find(a) != string::npos;
}

const int N=1e6+123;
bitset<N> isprime;
vector<int>prime;
void primegen(){
    //n+=100;
    isprime[2]=1;prime.push_back(2);
    for(int i=3;i<=N;i+=2)isprime[i]=1;
    for(int i=3;i<sqrt(N);i+=2)
    {
        if(isprime[i]==1)
        {
            for(int j=i*i;j<=N;j+=(i+i))isprime[j]=0;
        }
    }
    for(int i=3;i<=N;i+=2)
    {
        if(isprime[i])
        {
            prime.push_back(i);
        }
    }
}
long long phi(ll n){
    ll ret = n;
    for( auto p : prime){
        if(1LL*p*p > n || n == 0) break;
        if(n % p == 0){
            ret /= p;
            ret *= (p-1);
            while(n % p == 0) n /= p;
        }
    }
    if(n > 1){
        ret /= n;
        ret *= (n-1);
    }
    return ret;
}
/*
min heap with priority queue:
priority_queue<ll,vector<ll>,greater<ll>> minHeap;
*/

//const int N = 200005;
vector<int> adj[N];
vector<bool> visited(N,0);

bool isCycleComponent;
int nodes=0, edges=0;

void dfs(int u) {
    visited[u] = true;
    nodes++;
    edges += adj[u].size();
    for (int v : adj[u]) {
        if (!visited[v]) {
            dfs(v);
        }
    }
}

int countCycleComponents(int n) {
    int cycleCount = 0;
    for (int i = 1; i <= n; i++) {
        if (!visited[i]) {
            nodes = 0;
            edges = 0;
            dfs(i);  
            edges /= 2;
            if (edges == nodes && nodes > 2) {
                cycleCount++;
            }
        }
    }
    return cycleCount;
}

ll my_lower_bound(const vector<ll>& v, ll X) {
    ll n = v.size();
    ll low = 0;
    ll high = n; 
    ll ans = n;  

    while (low < high) {
        
        ll mid = low + (high - low) / 2;

        if (v[mid] >= X) {
          
            ans = mid;
            high = mid; 
        } else {
            
            low = mid + 1; 
        }
    }
    return ans;
}


ll my_upper_bound(const vector<ll>& v, ll X) {
    ll n = v.size();
    ll low = 0;
    ll high = n; 
    ll ans = n; 

    while (low < high) {
        
        ll mid = low + (high - low) / 2;

        if (v[mid] > X) {
            
            ans = mid;
            high = mid; 
        } else {
            
            low = mid + 1; 
        }
    }
    return ans;
}


ll maxSubarraySum(vector<ll> &arr){
    ll res = arr[0];           
    ll maxEnding = arr[0];     
    for (ll i = 1; i < arr.size(); i++) {
        maxEnding = max(arr[i], maxEnding + arr[i]);
        res = max(res, maxEnding);
    }
    return res;
}


bool isPowerOfTwo(ll n) {
    if (n <= 0) {
        return false;
    }
    return (n & (n - 1)) == 0;
}


ll dist[N];
void diameter(ll n, ll par){
    for(auto u:adj[n]){
        if(u!=par){
            dist[u]=dist[n]+1;
            diameter(u,n);
        }
    }
}
ll subtree_size[N];
void subtree_size_calculator(ll child,ll parent){
    subtree_size[child]=1;
    for(auto u:adj[child]){
        if(u==parent)
            continue;
        subtree_size_calculator(u,child);
        subtree_size[child]+=subtree_size[u];
    }
}
//sorting a vector of pair where first value will be in increasing order and second value will be in decreasing order
bool custom_sort(const pair<pair<ll, ll>, ll>& a, const pair<pair<ll, ll>, ll>& b){
    if (a.first.first != b.first.first) {
        return a.first.first < b.first.first;
    }
    return a.first.second > b.first.second;
}
const int fc=3e5+10;
int fact[fc];
void factorial(){
    fact[0]=1;
    for(ll i=1;i<=fc;i++){
        fact[i]=((fact[i-1]%MOD)*(i%MOD))%MOD;
    }
}

vll divisors(ll n){
    vll v;
    for(ll i=1;i*1LL*i<=n;i++){
        if(n%i==0){
            ll a=i;
            ll b=n/i;
            if(a==b){
                v.pb(a);
                continue;
            }
            else{
                v.pb(a);
                v.pb(b);
            }
        }
    }

    return v;
}


void solve(){
    ll x;cin>>x;
    ll y;cin>>y;
    ll ans=-1;
    for(ll i=1;i<=100;i++){
        if(i%x!=0 && i%y!=0){
            ans=i;
            break;
        }
    }
    cout<<ans<<endl;
}
 



int main() {
    // primegen();
    ll t;cin >> t;while (t--)
     
    {
        //primegen(1e6);
        //freopen("input.txt", "r", stdin);
        //freopen("output.txt", "w", stdout);
        solve();
    }
    return 0;
}