#include <bits/stdc++.h>

using namespace std;

bool isPrime(int num) { if (num < 2) return false; for (int i = 2; i <= sqrt(num); i++) { if (num % i == 0) return false; } return true; }

int main() { int S; cin >> S; int maxProduct = 0; for (int i = 2; i <= S / 2; i++) { if (isPrime(i) && isPrime(S - i)) { maxProduct = max(maxProduct, i * (S - i)); } } cout << maxProduct << endl; return 0; }