#include <iostream>
#include <algorithm>
using namespace std;

int main() {
  ios_base::sync_with_stdio(0); cin.tie(0);
  int tt; cin >> tt; while (tt--) {
    int n, m; cin >> n >> m;
    int G = __gcd(n, m);
    int ans = G;
    for (int i = 2; i * i <= G; i++) {
      if (G % i == 0) { ans = i; break; }
    }
    cout << (ans == 1 ? -1 : ans) << '\n';
  }
  return 0;
}