#include <iostream>
#include <utility>
#include <vector>
#include <string>
#include <cmath>
#include <algorithm>
#include <functional>
#include <iomanip>
#include <map>
#include <set>
#include <queue>
using namespace std;


int main(int argc, char const *argv[])
{
  int N; cin >> N;
  bool _prime[20010];
  auto _era = [&]()
  {
    for(int i=0;i<=20010;++i)_prime[i] = true;
    _prime[0] = _prime[1] = false;
    for(int i=2;i*i <= 20010;++i)
    {
      if(_prime[i])
      {
        for(int j=i*i;j<=20010; j += i)
        {
          _prime[j] = false;
        }
      }
    }
  };
  _era();
  vector<int> primes;
  for(int i=0;i<=N;++i)if(_prime[i])primes.emplace_back(i);

  vector<int> dp(N+1,-1);
  dp[0] = 0;
  auto chmax = [](int &x, int y) 
  {
    if(x < y)x = y;
    return x;
  };

  for(auto &pri : primes)
  {
    for(int j=N;j>=0;--j)
    {
      if(dp[j] != -1 && j + pri <= N)
      {
        chmax(dp[j+pri] , dp[j] + 1);
      }
    }
  }

  std::cout << dp[N] << std::endl;
}