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

int main(){
    int t;
    cin >> t;
    while(t--){
        int x, y;
        cin >> x >> y;
        if(x < y){
            for(int i = x; i <= 101; i++){
            if(i % x != 0 && i % y != 0 && i < 101){
                cout << i << "\n";
                break;
            }
            if(i == 101){
                cout << "-1" << "\n";
                break;
            }
        }
        }
        else{
            for(int i = y; i <= 101; i++){
            if(i % x != 0 && i % y != 0 && i < 101){
                cout << i << "\n";
                break;
            }
            if(i == 101){
                cout << "-1" << "\n";
                break;
            }
        }
        }
    }
}