#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

const ll MX = 10'000'010;
vector<ll> vs;

void init() {
  vector<bool> is_prime(MX + 10, true);
  is_prime[0] = false;
  is_prime[1] = false;
  for (ll i = 2; i <= MX; i++) {
    if (is_prime[i]) {
      if (is_prime[i - 2]) {
        vs.push_back(i * (i - 2));
      }
      for (ll j = i * 2; j <= MX; j += i) {
        is_prime[j] = false;
      }
    }
  }
}

void solve() {
  ll n;
  cin >> n;
  auto iter = lower_bound(vs.begin(), vs.end(), n);
  if (iter == vs.end())
    iter--;
  while (n < *iter) {
    if (iter == vs.begin()) {
      cout << "-1\n";
      return;
    }
    iter--;
  }
  cout << *iter << '\n';
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  init();
  int T = 1;
  cin >> T;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}