/* -*- coding: utf-8 -*-
 *
 * 458.cc: No.458 異なる素数の和 - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 20000;

/* typedef */

typedef vector<int> vi;

/* global variables */

bool primes[MAX_N + 1];
int dp[MAX_N + 1];

/* subroutines */

void gen_primes(int maxp, vi &pnums) {
  memset(primes, true, sizeof(primes));
  primes[0] = primes[1] = false;

  int p;
  for (p = 2; p * p <= maxp; p++)
    if (primes[p]) {
      pnums.push_back(p);
      for (int q = p * p; q <= maxp; q += p) primes[q] = false;
    }
  for (; p <= maxp; p++)
    if (primes[p]) pnums.push_back(p);
}

/* main */

int main() {
  vi pnums;
  gen_primes(MAX_N, pnums);

  int n;
  cin >> n;

  memset(dp, -1, sizeof(dp));
  dp[0] = 0;
  
  for (vi::iterator vit = pnums.begin(); vit != pnums.end(); vit++) {
    int &p = *vit;
    if (p > n) break;
    for (int i = n - p; i >= 0; i--)
      if (dp[i] >= 0) {
	int d0 = dp[i] + 1;
	if (dp[i + p] < d0) dp[i + p] = d0;
      }
  }
  printf("%d\n", dp[n]);
  return 0;
}