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

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

int dp[20001];

int main() {
    for (int i = 0; i <= 20000; i++) {
        dp[i] = -20000;
    }
    dp[0] = 0;
    for (int i = 2; i <= 20000; i++) {
        if (isPrime(i)) {
            for (int j = 20000 - i; j >= 0; j--) {
                dp[i + j] = max(dp[i + j], dp[j] + 1);
            }
        }
    }

    int n;
    cin >> n;
    cout << max(-1, dp[n]) << endl;
}