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

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    ll t;
    cin>>t;
    while(t--){
        ll x,y;
        cin>>x >>y;
        ll ans=-1;
        for(int i=2; i<=100; i++){
            if(i%x!=0 && i%y!=0){
                ans=i;
                break;
            }

        }
        cout<<ans <<endl;
    }

    return 0;
}