#include <bits/stdc++.h>

using namespace std;

int main() {
  const int MAX_N = 20010;
  vector<int> prime;
  vector<bool> is_prime(MAX_N, true);
  is_prime[0] = is_prime[1] = false;
  for(int i = 2; i <= MAX_N; ++i) {
    if(!is_prime[i]) continue;
    prime.push_back(i);
    for(int j = 2*i; j <= MAX_N; j += i) is_prime[j] = false;
  }
  int N;
  cin >> N;
  vector<int> dp(N+1, -1);
  dp[0] = 0;
  for(int p : prime) {
    for(int j = N; j >= p; --j) {
      if(dp[j-p] == -1) continue;
      dp[j] = max(dp[j], dp[j-p]+1);
    }
  }
  cout << dp[N] << endl;

  return 0;
}