#define _USE_MATH_DEFINES
#include <iostream>
#include <iomanip>
#include <map>
#include <stack>
#include <vector>
#include <string>
#include <cmath>
using namespace std;
const int MOD = 1e9 + 7;

vector<int> prime;

void sieve(int n){
    bool isPrime[n + 1];
    for(int i = 0; i <= n; i++)isPrime[i] = false;
    isPrime[0] = true;
    isPrime[1] = true;
    for(int i = 2; i <= n; i++){
        if(!isPrime[i]){
            prime.push_back(i);
            for(int j = i; j <= n; j += i){
                isPrime[j] = true;
            }
        }
    }
}
int main() {
    int n;
    cin >> n;
    sieve(n);

    vector<int> dp(n + 1, 0);

    dp[0] = 1;
    for(int i = 0; i < prime.size(); i++){
        for(int j = n; j >= 0; j--){
            if(dp[j] > 0){
                if(j + prime[i] > n)continue;
                else dp[j + prime[i]] = max(dp[j] + 1, dp[j + prime[i]]);
            }
        }
    }

    if(dp[n] == 0)cout << -1 << endl;
    else cout << dp[n] - 1 << endl;
}