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

using ll = long long;
using P = pair<int, int>;

const int MAX = 2e4 + 10;

bool not_prime[MAX];
vector<int> prime;
vector<int> num(MAX, -1);

void eratosthenes() {
  not_prime[0] = not_prime[1] = true;
  for (int i = 2; i * i <= MAX; i++) {
    for (int j = i; i * j <= MAX; j++) {
      not_prime[i*j] = true;
    }
  }
}

int main() {
  int N;
  cin >> N;

  eratosthenes();
  for (int i = 0; i <= MAX; i++) {
    if (!not_prime[i]) prime.push_back(i);
  }

  // DPで数え上げ
  num[0] = 0;
  for (int i = 0; i < prime.size(); i++) {
    for (int j = MAX; j >= prime[i]; j--) {
      if (num[j - prime[i]] == -1) continue;
      num[j] = max(num[j], num[j - prime[i]] + 1);
    }
  }

  // 解答
  cout << num[N] << endl;
  return 0;
}