#include <bits/stdc++.h>
using namespace std;
int main()
{
    int t;
    cin >> t;
    while (t--)
    {
        int x,y;
        cin>>x>>y;
        bool find=false;
        int b=0;
        for(int i=1;i<=100;i++){
            if(i%x!=0 && i%y!=0){
                b=i;
                find = true;
                break;
            }
        }
        if(find) cout<<b<<endl;
        else cout<<"-1"<<endl;
        
    }
}