#include "bits/stdc++.h"
#define _CRT_SECURE_NO_WARNINGS
#define rep(i,n) for(int i = 0;i < n;i++)
#define REP(i,n,k) for(int i = n;i < k;i++)
#define P(p) cout << (p) << endl;
#define sP(p) cout << setprecision(15) << fixed << p << endl;
#define vi vector<int>
#define mp(a,b) make_pair(a,b)
using namespace std;typedef long long ll;typedef unsigned long long ull;int dx[] = { 1, -1 , 0 , 0};int dy[] = { 0,  0,  1, -1};

bool isPrime(int n) {
  if (n <= 1)return false;
  if (n == 2)return true;
  if (n % 2 == 0)return false;
  for (int i = 3; i*i <= n; i += 2) {
    if (n%i == 0)return false;
  }
  return true;
}

void solve() {
  int n;
  cin >> n;
  vi v(n+1,0),prime;
  prime.push_back(2);
  v[2] = 1;
  for(int i = 3;i <= n;i += 2){
    if(isPrime(i)){
      v[i] = 1;
      prime.push_back(i);
    }
  }
  sort(prime.begin(),prime.end());
  rep(i,prime.size()){
    for(int j = n;j-prime[i] >= 1;j--){
      if(j-prime[i] != prime[i]){
	if(v[j-prime[i]] != 0){
	  v[j] = max(v[j],v[j-prime[i]] + 1);
	}
      }
    }
  }
  P(v[n] != 0 ? v[n] : -1);
}

int main() {
	solve();
	return 0;
}