#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)

vector<bool> psieve(int n) {
  vector<bool> pr(n);
  for (int i = 2; i < n; i++)
    pr[i] = true;
  for (int i = 2; i * i < n; i++) {
    if (!pr[i]) continue;
    for (int j = i * i; j < n; j += i)
      pr[j] = false;
  }
  return pr;
}

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

  int n;
  cin >> n;
  auto pr = psieve(n+1);
  vector<int> dp(n+1, -1);

  dp[0] = 0;
  for (int x = 2; x <=n ; x++) {
    if (!pr[x]) continue;
    for (int i = n; i >= 0; i--) {
      if (i-x >= 0 && dp[i-x] != -1)
        dp[i] = max(dp[i], dp[i-x] + 1);
    }
  }
  
  if (dp[n] < 1)
    cout << -1 << endl;
  else
    cout << dp[n] << endl;
  
  return 0;
}