#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define loop(__x, __start, __end) for(int __x = __start; __x < __end; __x++)
template <class T> bool chmax(T &a, T b) { if (a < b) {a = b; return true; } return false; }
template <typename T>  ostream& operator<<(ostream& os, const vector<T>& v)  {  for (int i = 0; i < v.size(); ++i) {  os << v[i];  if (i != v.size() - 1)  os << ' ';  } return os;  }


vector<ll> prime(int n) {
  vector<bool> ok(n+1, true);
  ok[0] = ok[1] = false;
  for (int i=1; i*i<=n; i++) {
    if (!ok[i]) continue;

    for (int j=i*2; j<=n; j+=i) {
      ok[j] = false;
    }
  }

  vector<ll> ret;
  for (int i=2; i<=n; i++)
    if (ok[i]) ret.push_back(i);
  return ret;
}


int main() {
  int n; cin >> n;
  auto P = prime(n);
  vector<ll> dp(n+1, -1);
  dp[0] = 0;
  // cout << dp << endl;
  for (auto p: P) {
    // cout << p << endl;
    for (int i=n; i>=0; i--) {
      if (dp[i]==-1) continue;
      if (i+p<=n) {
        chmax(dp[i+p], dp[i] + 1);
        // cout << "\t" << i << "\t" << dp << endl;
      }
    }
  }
  cout << dp[n] << endl;
  return 0;
}