#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;

auto sieve(int n){
    int p = 0;
    vector<int> prime;
    vector<bool> is_prime(n+1,true);
    is_prime[0] = is_prime[1] = false;
    for(int i = 2 ; i <= n ; i++){
        if(is_prime[i]){
            prime.push_back(i);
            for(int j = 2*i; j <= n; j += i){
                is_prime[j] = false;
            }
        }
    }
    return prime;
}

int main(){
  int n;
  cin >> n;
  auto table = sieve(n);
  int m = table.size();
  vector<int> dp(n+1,-1);
  dp[0] = 0;
  for (int i = 0; i < m; i++) {
    auto next = dp;
    for (int j = 1; j <= n; j++) {
      if (j - table[i] >= 0 && dp[j - table[i]] != -1) next[j] = max(dp[j], dp[j - table[i]] + 1); 
    }
    dp = next;
  }
  cout << dp[n] << endl;
  return 0;
}