#include <iostream>
#include <vector>
using namespace std;

/* dp[i]は、整数iの素数での和の数のmax */
int dp[40001];

vector<int> makeBitPrimes(int n){
    vector<int> v(n+1, 1); 
    v[0] = v[1] = 0;
    for(int  i = 2; i*i <= n; i++){
        if(v[i]==1){
            int j = i + i;
            while (j <= n){
                v[j] = 0;
                j = j + i;
            }
        }
    }
    
    return v;
}

int main(void){
    // Your code here!
    int N;
    vector<int> v = makeBitPrimes(40000);
    cin >> N;

    for(int i = 0; i <= 40000; i++) {
        dp[i] = -1;
    }
    
    dp[0] = 0;
   
    for(int i = 1; i <= 20000; i++){
        if(v[i] == 0) continue;
        for(int j = N; j >= 0; j--){
            if(i+j <= N && dp[j] != -1) dp[i+j] = max(dp[i+j], dp[j] +1);
        }
    }
    
    cout << dp[N] << endl;
}