#include <bits/stdc++.h>

using namespace std;

const int MAX_N = 20010;
bool is_prime[MAX_N];
vector<int> prime;
int dp[2][MAX_N];

void sieve() {
  fill(is_prime, 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 main() {
  sieve();

  int n;
  cin >> n;

  int turn = 0;
  fill(dp[turn], dp[turn] + MAX_N, -1);
  dp[turn][0] = 0;
  for (int i = 0; i < prime.size() && prime[i] <= n; i++) {
    for (int j = 0; j <= n; j++) {
      if (j - prime[i] < 0) {
        dp[!turn][j] = dp[turn][j];
      } else if (dp[turn][j - prime[i]] >= 0) {
        dp[!turn][j] = max(dp[turn][j], dp[turn][j - prime[i]] + 1);
      }
    }
    turn = !turn;
  }
  cout << dp[turn][n] << endl;

  return 0;
}