#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main()
{
    //freopen("input.txt","r", stdin);
    int t;
    cin >> t;
    while (t--){
       ll x, y;
       cin >> x >> y;
       int pr = 0;
       for ( int i = 1; i <= 100; i++){
          if ( i % x && i % y) { cout << i << endl; pr =1; break;}
       }
       if ( pr == 0) cout<< -1 << endl;
    }
    return 0;
}