#define _GLIBCXX_DEBUG
#define ll long long
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;

int main(){
  int N; cin >> N;
  vector<int> dp(N*3, -1);
  dp[0] = 0;
  for(int i = 2; i <= N; i++){
    bool flag = true;
    for(int j = 2; j*j <= i; j++){
      if(i%j == 0){
        flag = false;
        break;
      }
    }
    if(flag){
      for(int j = N; j >= 0; j--){
        if(dp[j] != -1){
          dp[j+i] = max(dp[j]+1, dp[j+i]);
        }
      }
    }
  }
  cout << dp[N] << endl;
}