#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
using T = tuple<int, int, int>;
#define al(a) a.begin(), a.end()
#define ral(a) a.rbegin(), a.rend()
#define sz(a) (int)a.size()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define db(a, b) cout << #a << ": " << a << " " << #b << ": " << b << endl;

int main() {
  int n;
  cin >> n;

  vector<int> f(n + 1), a;
  f[0] = f[1] = -1;
  for (int i = 2; i <= n; ++i) {
    if (f[i]) continue;
    a.push_back(i);
    for (int j = i + i; j <= n; j += i) { f[j] = i; }
  }

  vector<int> dp(n + 1, -1);
  dp[0] = 0;
  int m = sz(a);
  rep(i, m) {
    // db(i, a[i]);
    drep(j, n) {
      if (dp[j] == -1) continue;
      if (j + a[i] > n) continue;
      dp[j + a[i]] = max(dp[j + a[i]], dp[j] + 1);
    }
  }

  cout << dp[n] << endl;
  return 0;
}