#include<bits/stdc++.h>
#define int long long
using namespace std;

signed main(){

    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);

  //  freopen("input.txt","r",stdin); freopen("output.txt","w",stdout);

    int t;
    cin >> t;
    while(t-->0){
        int x, y;
        cin >> x >> y;
        bool flag = 0;
        for(int i = 1; i <= 100; ++i){
            if(i % x != 0 && i % y != 0){
                cout << i << '\n';
                flag = 1;
                break;
            }
        }
        if(!flag)cout << -1 << '\n';
    }

    return 0;
}