#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;
using ll = long long int;
#define chmax(x,y)  (x) = ((x) > (y)) ? (x) : ((x) = (y));
#define chmin(x,y)  (x) = ((x) < (y)) ? (x) : ((x) = (y));


int main(int argc, char const *argv[])
{
  int N; cin >> N;
  vector<int> prime;
  auto eratos = [&](int x)
  {
    vector<int> v(x+1,1);
    v[0] = v[1] = 0;
    for(int i=2;i*i<=x;++i)
    {
      if(v[i])
      {
        //std::cout << i << std::endl;
        for(int j=i*i;j<=x;j+=i)
        {
          v[j] = 0;
        }
      }
    }
    for(int i=2;i<=x;++i)
    {
      if(v[i])prime.push_back(i);
    }
  };
  eratos(N);
  vector<int> dp(N+2,-1);
  dp[0] = 0;
  for(auto &p : prime)for(int i=N;i>=0;--i)
  {
    if(dp[i] != -1 && i+p <= N)chmax(dp[i+p],dp[i]+1);
  }
  std::cout << dp[N] << std::endl;
}