#include <bits/stdc++.h> using namespace std; int S; int ma;

bool check(int n) { if (n < 2) return false; for (int i = 2; i * i <= n; ++i) if (n % i == 0) return false; return true; }

int main() { cin >> S; for (int i = 1; i <= S; ++i) if (check(i)) if (check(S - i)) if (i * (S - i) > ma) ma = i * (S - i); cout << ma; return 0; }