#include <bits/stdc++.h>
//#include <atcoder/all>

using namespace std;
//using namespace atcoder;
using usize = ::std::size_t;
//using u64 = ::std::int_least64_t;
using u64 = long long;
static constexpr u64 Inf = ::std::numeric_limits<u64>::max() / 2;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a = b; return 1; } return 0; }

vector< bool > prime_table(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]) continue;
    for(int j = i + i; j <= n; j += i) {
      prime[j] = false;
    }
  }
  return prime;
}


int main(int argc, char *argv[])
{
    std::ifstream in("in.txt");
    std::cin.rdbuf(in.rdbuf());
    
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    int N;
    cin >> N;
    vector<int> dp(N+1,-1);
    dp[0] = 0;
    auto t = prime_table(N);
    
    for (int i = 0; i <= N; i++) {
        if(!t[i]) continue;
        for (int j = N; j >= i; j--) {
            if(dp[j - i] == -1) continue;
            dp[j] = max(dp[j], dp[j - i] + 1);
        }
    }
    
    cout << dp[N] << endl;
    
    return 0;
    
}