#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <numeric>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <utility>
#include <sstream>
#include <complex>
#include <fstream>
#include <bitset>
#include <time.h>
#include <tuple>
#include <iomanip>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
typedef vector<ll> V;
typedef complex<double> Point;

#define PI acos(-1.0)
#define EPS 1e-10
const ll INF = 1e16;
const ll MOD = 1e9 + 7;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define rep(i,N) for(int i=0;i<(N);i++)
#define ALL(s) (s).begin(),(s).end()
#define EQ(a,b) (abs((a)-(b))<EPS)
#define EQV(a,b) ( EQ((a).real(), (b).real()) && EQ((a).imag(), (b).imag()) )
#define fi first
#define se second
#define N_SIZE (1LL << 20)
#define NIL -1

ll sq(ll num) { return num*num; }
ll mod_pow(ll x, ll n) {
	if (n == 0)return 1;
	if (n == 1)return x%MOD;
	ll res = sq(mod_pow(x, n / 2));
	res %= MOD;
	if (n % 2 == 1) {
		res *= x;
		res %= MOD;
	}
	return res;
}
ll mod_add(ll a, ll b) { return (a + b) % MOD; }
ll mod_sub(ll a, ll b) { return (a - b + MOD) % MOD; }
ll mod_mul(ll a, ll b) { return a*b % MOD; }

ll n;

vector<int> prime;
bool is_prime[20000 + 1];

int sieve(int n){
	int p = 0;
	for (int i = 0; i <= n; i++)is_prime[i] = 1;
	is_prime[0] = is_prime[1] = 0;
		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] = 0;
		}
	}
	return p;
}

ll dp[20000+1][2];

int main(){
	cin >> n;
	sieve(20000);
	rep(i,20000+1)rep(j,2)dp[i][j] = -1;
	dp[0][0] = 0;
	rep(i,prime.size()){
		rep(j,n+1){
			if(dp[j][i%2] == -1)continue;
			if(j+prime[i] <= n){
				dp[j+prime[i]][(i+1)%2] = max(dp[j+prime[i]][i%2],dp[j][i%2]+1);
			}
			dp[j][(i+1)%2] = max(dp[j][(i+1)%2],dp[j][i%2]);
		}
	}
	cout << dp[n][n%2] << endl; 
}