#pragma GCC optimize ("O3")
#pragma GCC target ("avx")
#include <bits/stdc++.h>
using namespace std;

bitset<20001> p;
int8_t dp[20001];

int main() {
    for (int i = 1; i <= 20000; i++) {
        dp[i] = INT8_MIN;
    }
    for (int i = 2; i <= 20000; i++) {
        for (int j = i * i; j <= 20000; j += i) {
            p[j] = true;
        }
        if (!p[i]) {
            for (int j = 20000 - i; j >= 0; j--) {
                dp[i + j] = max<int8_t>(dp[i + j], dp[j] + 1);
            }
        }
    }

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