#include <bits/stdc++.h>

using namespace std;

#define int int64_t
#define el '\n'

void run_case(int tc) {
  int x, y;
  cin >> x >> y;
  for (int i = 1; i <= 100; i++) {
    if ((i%x) && (i%y)) {
      cout << i << el;
      return;
    }
  }
  cout << "-1\n";
}

int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int _t = 1;
  cin >> _t;
  for (int i = 1; i <= _t; i++) {
    run_case(i);
  }
}