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

#define ll long long
#define endl '\n'

void solve() {
    int x, y; cin >> x >> y;
    for(int i = 1; i <= 100; ++i) {
        if((i % x != 0) and (i % y != 0)) {
            cout << i << endl;
            return;
        }

    }
    cout << -1 << endl;
}

int32_t main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int t = 1;
    cin >> t; while(t--) solve();
    
    return 0;
}