#include<bits/stdc++.h>
#define ll long long
#define cy cout<<"YES"<<endl
#define cn cout<<"NO"<<endl
#define srt sort(v.begin(),v.end())
#define pb push_back
using namespace std;

void rs(){
    int x,y;
    cin>>x>>y;

    int c=-1;

    if(x==1 || y==1){
        cout<<-1<<endl;
        return;
    }

    for(int i=1;i<100;i++){
        if(i%x!=0 && i%y!=0){
            c=i;
            break;
        }
    }
    cout<<c<<endl;
}

int main(){
    int t;
    cin>>t;

    while(t--){
        rs();
    }
    return 0;
}