#include <bits/stdc++.h>

#pragma GCC optimize("Ofast")
using namespace std;

void solve(int cs) {
  int a, b;
  cin >> a >> b;
  int g = __gcd(a, b);
  if (g == 1) {
    cout << "-1\n";
  } else {
    for (int i = 2; i * i <= g; i++) {
      if (g % i == 0) {
        cout << i << "\n";
        return;
      }
    }
    cout << g << "\n";
  }
  
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int tc = 1;
  cin >> tc;
  for (int cs = 1; cs <= tc; cs++) {
    solve(cs);
  }
  return 0;
}