#include <iostream>
#include <string>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <map>
#include <cmath>
#include <queue>
#include <utility>
#include <functional>
#include <deque>
#include <cctype>
#include <stack>
#include <bitset>
#include <set>

using ll = long long;
using namespace std;
typedef unsigned long long ull;
typedef pair<ll, ll> P;

const ll MOD = 1000000007;
const ll INF = 1 << 30;
const ll INF2 = 9000000000000000000LL;
const double INF3 = 900000000000000;
const int dx[4] = { 1,0,-1,0 }, dy[4] = { 0,1,0,-1 };
const int tx[8] = { -1,0,1,-1,1,-1,0,1 }, ty[8] = { -1,-1,-1,0,0,1,1,1 };
#define ALL(x) (x).begin(),(x).end()

bool bpr[20010];

void sieve(int n) {
	for (int i = 0;i <= n;i++)bpr[i] = true;
	bpr[0] = bpr[1] = false;
	for (int i = 2;i <= n;i++) {
		if (bpr[i]) for (int j = i * 2;j <= n;j += i)bpr[j] = false;
	}
}

int main() {
	int m, dp[20010] = { 0 };
	vector<int>p;
	cin >> m;
	for (int i = 0;i <= 20010;i++)dp[i] = -1;
	dp[0] = 0;
	sieve(20010);
	for (int i = 0;i <= m;i++) {
		if (bpr[i])p.push_back(i);
	}
	for (int i = 0;i < p.size();i++) {
		for (int j = m;j >= 0;j--) {
			if (p[i] + j <= m&& dp[j] != -1)dp[p[i] + j] = max(dp[p[i] + j], dp[j] + 1);
		}
	}
	cout << dp[m] << endl;
}