#include<bits/stdc++.h>
using namespace std;


int A[20001];
int memo[20001];

int main() {
	memset(memo, -1, sizeof(memo));
	memo[0] = 0;
	for(int i = 2; i <= 20000; ++i){
		if(!A[i]){
			for(int j = i * 2; j <= 20000; j += i){
				A[j] = 1;
			}
			for(int j = 20000; j >= i; --j){
				if(memo[j - i] >= 0){
					memo[j] = max(memo[j], memo[j - i] + 1);
				}
			}
		}
	}
	int n;
	cin >> n;
	cout << memo[n] << endl;
	return 0;
}