#include <bits/stdc++.h>
using namespace std;

#define rep(i, j, n) for(int i=j;i<n;++i)
#define all(i) i.begin(),i.end()
#define rall(i) i.rbegin(),i.rend()
#define INF 1e9
const int mod = 1e9 + 7;

typedef long long i64;
typedef pair<int, int> pi;

template <class T> using vt = vector<T>;
template <class T> using vvt = vector<vector<T>>;

i64 gcd(i64 n, i64 m) {return (m == 0? n : gcd(m, n % m));}
i64 lcm(i64 n, i64 m) {return (n / gcd(n, m) * m);}
int dx[] = {0, 1, 0, -1};
int dy[] = {1, 0, -1, 0};

bool PrimeNumber(int n) {
  if(n < 2) return false;
  for(int i = 2; i * i <= n; ++i) {
    if(n % i == 0) return false;
  }
  return true;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n;
  cin >> n;

  vt<int> vec;
  rep(i, 2, n + 1) {
    if(PrimeNumber(i)) vec.push_back(i);
  }

  vt<int> dp(n + 1, -1);
  dp[0] = 0;
  rep(i, 0, vec.size()) {
    for(int j = n; j >= 0; --j) {
      if(j >= vec[i] && dp[j - vec[i]] != -1) dp[j] = max(dp[j], dp[j - vec[i]] + 1);
    }
  }
  cout << dp[n] << endl;
}