#include <bits/stdc++.h>

using namespace std;

bool prime[20002];
int dp[20002];
int n;
int main() {
  cin >> n;
  for(int i = 2; i <= n; i++) {
    if(prime[i]) continue;
    for(int j = i + i; j <= n; j += i) {
      prime[j] = true;
    }
  }
  fill(dp,dp+n+1,-1);
  dp[0] = 0;

  for(int i = 2; i <= n; i++) {
    if(prime[i]) continue;
    for(int j = n; j >= 0; j--) {
      if(j + i >  n || dp[j] < 0) continue;
      dp[j+i] = max(dp[j+i],dp[j] + 1);
    }
  }

  if(dp[n]) cout << dp[n] << endl;
  else cout << -1 << endl;
}