# include <iostream>
# include <algorithm>
# include <vector>
# include <string>
# include <set>
# include <map>
# include <cmath>
# include <iomanip>
# include <functional>
# include <utility>
# include <stack>
# include <queue>
# include <list>
# include <bitset>
# include <complex>
# include <numeric>
# include <tuple>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
constexpr int INF = 2000000000;
constexpr int HINF = INF / 2;
constexpr double DINF = 100000000000000000.0;
constexpr long long LINF = 9223372036854775807;
constexpr long long HLINF = 4500000000000000000;
const double PI = acos(-1);
int dx[4] = { 0,1,0,-1 }, dy[4] = { 1,0,-1,0 };
#define ALL(x)    (x).begin(),(x).end()
#define UNIQ(c)   (c).erase(unique(ALL((c))), end((c)))
#define mp        make_pair
#define eb        emplace_back
typedef pair<LL, double> P;
typedef pair<P, P> PP;

int n, dp[20202];

vector<int> prime;
void MakePrime(int n) {
	prime.emplace_back(2);
	for (int i = 3; i < n; i += 2) {
		bool a = false;
		for (int j = 3; j <= std::sqrt(i); j += 2) {
			if (i%j == 0) {
				a = true;
			}
		}
		if (a == false) {
			prime.emplace_back(i);
		}
	}
}


int main() {
	cin >> n;
	for (int i = 0; i < 20202; i++)dp[i] = -1;
	dp[0] = 0;
	MakePrime(20000);
	for (int i = 0; i < prime.size(); i++) {
		for (int j = n; j >= 0; j--) {
			if (j + i <= n&&dp[j] != -1)dp[prime[i]+j] = max(dp[prime[i] + j], dp[j] + 1);
		}
	}
	cout << dp[n] << endl;
}