#include <algorithm>
#include <iostream>
#include <vector>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;

#define MOD 1000000007
#define REP(i, N) for (int i = 0; i < N; ++i)
#define REP1(i, N) for (int i = 1; i <= N; ++i)
#define RREP(i, N) for (int i = N - 1; i >= 0; --i)
#define ALL(a) a.begin(), a.end()

int main() {
  bool is_prime[20001];
  REP(i, 20001) is_prime[i] = true;
  is_prime[0] = false, is_prime[1] = false;
  for (int i = 2; i * i <= 20000; i++) {
    if (is_prime[i]) {
      for (int j = 2; i * j <= 20000; j++) {
        is_prime[i * j] = false;
      }
    }
  }
  vector<int> prime;
  REP1(i, 20000) if (is_prime[i]) prime.push_back(i);
  int n;
  cin >> n;
  int dp[20001] = {};
  REP(i, 20001) dp[i] = -1;
  dp[0] = 0;
  for (auto p : prime) {
    for (int i = n; i >= 0; --i) {
      if (p + i <= n && dp[i] != -1) {
        dp[p + i] = max(dp[p + i], dp[i] + 1);
      }
    }
  }
  cout << dp[n] << endl;
  return 0;
}