#include <bits/stdc++.h>

using namespace std;

vector< bool > get_prime(int n)
{
  vector< bool > prime(n + 1, true);

  if(n >= 0) prime[0] = false;
  if(n >= 1) prime[1] = false;

  for(int i = 2; i * i <= n; i++) {
    if(prime[i]) {
      for(int j = i + i; j <= n; j += i) prime[j] = false;
    }
  }

  return prime;
}

int main()
{
  int N;
  cin >> N;
  vector< bool > prime = get_prime(N + 1);
  int dp[20001];
  memset(dp, -1, sizeof(dp));
  for(int i = 2; i <= N; i++) {
    if(!prime[i]) continue;
    for(int j = N - i; j >= 0; j--) {
      if(dp[j] == -1) continue;
      dp[j + i] = max(dp[j + i], dp[j] + 1);
    }
    dp[i] = max(dp[i], 1);
  }
  cout << dp[N] << endl;
}