#include <bits/stdc++.h>
using namespace std;
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
typedef long long ll;
// Welcome to my source code!

template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }

const int MAX_N = 1e5*3;

vector<int> prime;
bool is_prime[MAX_N];

void sieve(int n) {
    for (int i = 0; i <= n; i++) is_prime[i] = true;
    is_prime[0] = is_prime[1] = false;
    for (int i = 2; i <= n; i++) {
        if (is_prime[i]) {
            prime.push_back(i);
            for (int j = 2 * i; j <= n; j += i) is_prime[j] = false;
        }
    }
}

int main() {
    int n;
    cin >> n;
    sieve(n);
    int m = prime.size();
    int dp[MAX_N];
    fill(dp, dp+MAX_N, -1);
    dp[0] = 0;
    for (int i = 0; i < m; i++) {
        for (int j = n; j >= prime[i]; j--) {
            if (dp[j - prime[i]] != -1) chmax(dp[j], dp[j - prime[i]] + 1);
        }
    }
    cout << dp[n] << endl;
}