#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, one = -1, flag = 0;
  cin >> n;
  int arr[n];
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  sort(arr, arr + n);
  for (int i = 1; i < n; i++) {
    if (arr[i] % arr[0] != 0) {
      flag = 1;
      cout << one;
      break;
    }
  }
  if (flag == 0) {
    cout << arr[0];
  }
  return 0;
}
