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

int prime[20001];

void eratosthenes(int n)
{
	for (int i = 1; i <= n; i++)
	{
		prime[i] = 1;
	}

	prime[1] = 0;

	for (int i = 2; i <= n / 2; i++)
	{
		for (int j = 2; i * j <= n; j++)
		{
			prime[i*j] = 0;
		}
	}
}

int main()
{
	int n, dp[20001];

	vector<int> P;

	cin >> n;

	for (int i = 1; i <= n; i++)
	{
		dp[i] = -1;
	}

	dp[0] = 0;

	eratosthenes(n);

	for (int i = 1; i <= n; i++)
	{
		if (prime[i] == 1)
		{
			P.push_back(i);
		}
	}

	for (auto i : P)
	{
		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;
}