#include <iostream>
#include <algorithm>
using namespace std;
using i64 = long long;


int main(void) {
  int n; scanf("%d", &n);
  if(n == 1 || n == 4 || n == 6) { puts("-1"); return 0; }
  vector<bool> is_prime(n+1, true);
  is_prime[0] = is_prime[1] = false;
  int sq = sqrt(n);
  for(int i=2; i<=sq; ++i) {
    if(is_prime[i]) {
      for(int j=i*i; j<=n; j+=i) {
        is_prime[j] = false;
      }
    }
  }
  vector<int> primes;
  for(int i=2; i<=n; ++i) {
    if(is_prime[i]) { primes.push_back(i); }
  }
  int m = primes.size();


  vector<vector<int>> dp(m+1, vector<int>(n+1, -1)); // dp[m+1][n+1]
  dp[0][0] = 0;
  for(int i=0; i<m; ++i) {
    for(int acc=0; acc<=n; ++acc) {
      dp[i+1][acc] = max(dp[i+1][acc], dp[i][acc]);
      if(acc + primes[i] <= n) {
        dp[i+1][acc+primes[i]] = max(dp[i+1][acc+primes[i]], dp[i][acc] + 1);
      }
    }
  }
  int res = dp[m][n];
  printf("%d\n", res);

  return 0;
}