/**
    Author : Abdullah Al Mahdi
    CF Handle: abdmahdi56
    Leading University,Sylhet

    Submitted on:
*/
#include <bits/stdc++.h>
#define endl '\n'
#define yes cout << "YES\n"
#define no cout << "NO\n"
#define ll long long
#define vi vector<ll>
#define all(v) v.begin(), v.end()
#define loop(i,n) for(int (i) = 0; (i) < (n); (i)++)

using namespace std;

void Bismillah() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
}

void solve() {
    int x,y;
    cin>>x>>y;
    int ans=min(x,y)+1;
    bool ok=true;
    if(x==1 || y==1){
        cout<<-1<<endl;
        return ;
    }
    while(ok){
        if(ans %x!=0 && ans%y!=0 && ans<=100){
            ok =false;
            cout<<ans<<endl;
        }else ans++;
    }
}

int main() {
    Bismillah();
    int t;
    cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}