#include <bits/stdc++.h>

using namespace std;

class SieveOfEratosthenes {
 private:
  std::vector<int> sieve;

 public:
  SieveOfEratosthenes(int n) : sieve(n + 1) {
    std::iota(sieve.begin(), sieve.end(), 0);
    for (int i = 2; i * i < n + 1; i++) {
      if (sieve[i] != i) continue;
      for (int j = i * i; j < n + 1; j += i) {
        if (sieve[j] == j) sieve[j] = i;
      }
    }
  }

  bool is_prime(int x) const { return x != 0 && x != 1 && sieve[x] == x; }

  std::vector<int> factor(int x) const {
    std::vector<int> res;
    while (x > 1) {
      res.emplace_back(sieve[x]);
      x /= sieve[x];
    }
    return res;
  }
};

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int N;
  cin >> N;
  SieveOfEratosthenes soe(N);
  vector<int> primes;
  for (int i = 0; i < N + 1; i++) {
    if (soe.is_prime(i)) primes.emplace_back(i);
  }
  vector<int> dp(N + 1, -1);
  dp[0] = 0;
  for (int p : primes) {
    for (int x = N; x > -1; x--) {
      if (dp[x] != -1 && x + p < N + 1) dp[p + x] = max(dp[p + x], dp[x] + 1);
    }
  }
  cout << dp[N] << '\n';
  return 0;
}