#include<bits/stdc++.h>
using namespace std;
#define ll long long
int main(){
    ll t;
    cin >> t;
    while(t--){
        ll n,m;
        cin >> n >> m;
        ll k = 1;
        while(k<=101){
            if((k%n)!=0 && (k%m)!=0){
                break;
            }
            k++;
        }
        if(k>=101)cout << "-1\n";
        else cout << k << endl;
    }
}