#include <bits/stdc++.h>     //   All praise is due to Allah alone, and peace and blessings be
using namespace std;         //         upon him, after whom there is no other Prophet.

int32_t main() {
    cin.tie(0)->sync_with_stdio(false);

    int32_t Case = 1;    cin >> Case;
    for (int T = 1; T <= Case; T++) {

        int n, m; cin >> n >> m;
        int val = -1;
        for(int i = 2; i <= 100; i++) {
            if(i % n and i % m) {
                val = i; break;
            }
        }
        cout << val << '\n';
    }
    return 0;
}