#include <iostream>
#include <vector>

using namespace std;

#define chmax(a, b) a = (((a)<(b)) ? (b) : (a))
#define pb push_back
bool isprime[20010];
//エラトステネス
void eratos(int m){
    for (int i = 0; i <= m; ++i) isprime[i] = true;
    isprime[0] = isprime[1] = false;
    //iを残してiの倍数を消していく
    for (int i = 2; i <= m; ++i){
        if(isprime[i]){
            for (int j = 2 * i; j <= m; j += i){
                isprime[j] = false;
            }
        }
    }
}


vector<int> prime;
//dp[i] := 合計がjとなるときの最大値
int dp[20010];


int main(void){
    int n; cin >> n;
    for(int i = 0; i < n+1;i++) dp[i] = -1;
    eratos(20010);

    
    for(int i=(2);i<(20001);i++){
        if(isprime[i]){
            prime.pb(i);
        }
    }
    dp[0] = 0;

    for(auto u : prime){
        for (int j = n; j >= 0; --j){
            if(u + j <= n && dp[j] != -1){
                chmax(dp[u + j], dp[j] + 1);
            }
        }
    }
    printf("%d\n", dp[n]);
    return 0;
}