#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define testCase ll t; cin >> t; while (t--)
#define Iread ll n; cin >> n; for (ll i = 0; i < n; i++)
#define loop(n) for (ll i = 0; i < n; i++)
#define dbloop(n, m)  for (ll i = 0; i < n; ++i) for (ll j = 0; j < m; ++j)
#define dloop(n) for (ll i = 0, j = n - 1; i < j; ++i, --j)
#define arr(n) ll arr[n]
#define vi vector<ll>
#define ain(arr, n) for (ll i = 0; i < n; ++i) {cin >> arr[i]; }
#define vin(v) for (auto& i : v) cin >> i;
#define prnt(n) for (const auto& i : n) { cout << i << " "; } cout << "\n";
#define endl "\n"


// vi prime; 

// void sv() {
//     vi primes(102,1); 
//     primes[0] = primes[1] = 0; 

//     for (ll i = 2; i * i <= 101; i++) {
//         if (primes[i]) {
//             for (ll j = i * i; j <= 101; j+=i) {
//                 primes[j] = 0; 
//             }
//         }
//     }

//     for (ll i = 2; i <= 101; i++) {
//         if(primes[i]) prime.push_back(i); 
//     }
// }

//2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 101 
int main() {
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
//start
vi prime = {2,3,5,7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53 ,59 ,61, 67, 71, 73, 79, 83, 89, 97}; 
testCase {
        //sv(); 
        //prnt(prime); 
        // if (x == 1) {
            //     cout << "-1" << endl; 
            //     continue;
            // }
            // for (ll i = 1; i <= 100; i++) {
                //     if (i % x != 0 && i % y != 0) ans = i; 
                // }
        ll x,y; cin >> x >> y; 
        ll ans = -1; 
        for (ll i = 0; i < prime.size(); i++) {
            if (prime[i] % x != 0 && prime[i] % y  != 0) {
                ans = prime[i]; 
                break;
            }
        }
        (ans == -1) ? cout << "-1\n" : cout << ans << endl; 
    }
}