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

#define ll long long

void solve(){
    int x, y;
    cin >> x >> y;
    for(int i = 1 ; i <= 100 ; i++){
        if(i % x != 0 && i % y != 0){
            cout << i << '\n';
            return;
        }
    }   
    cout << "-1\n";
}

int main(){
    ios_base::sync_with_stdio(0), cin.tie(0);
    int t = 1;
    cin >> t;
    while(t--){
        solve();
    }
    return 0;
}