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

#ifdef LOCAL
#include "debug.h"
#else
#define dbg(...)
#endif

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

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

}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int t; cin >> t;while (t--)
    solve();
    return 0;
}