#include<bits/stdc++.h>
using namespace std;
#define ll long long
int main()
{
    ll t ;
    cin>>t;
    while(t--){
        ll x , y;
        cin>>x>>y;
        ll cnt=0;
        for(ll i=2 ; i<=100 ; i++){
            if(i%x!=0 && i%y!=0){
                cout<<i<<endl;
                cnt=1;
                break;
            }
        }
        if(cnt==0){
            cout<<-1<<endl;
        }
       }

}