#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>

using namespace std;

int main(void){
    int n;
    cin >> n;
    
    vector<int> pt(20001, 0);
    for (int i = 2; i < 20001; i++) {
        int j = i + i;
        while (j < 20001) {
            pt[j]++;
            j += i;
        }
    }
    vector<int> p;
    for (int i = 2; i < n+1; i++) if (!pt[i]) p.push_back(i); 
    
    vector<int> dp(20001, -1);
    dp[0] = 0;
    for (int i = 0; i < p.size(); i++) {
        for (int j = n; j >= 0; j--) {
            if (dp[j] == -1) continue;
            if (j+p[i] > n) continue;
            dp[j+p[i]] = max(dp[j+p[i]], dp[j] + 1);
        }
    }
    cout << dp[n] << endl;
}