#include <vector>
#include <iostream>

std::vector<int> sieve(int n)
{
	std::vector<bool> nums(n + 1, true);
	std::vector<int> primes;

	for (int i = 2; i *i <= n; i++)
	{
		if (nums[i])
		{
			for (int j = 2; i*j <= n; j++)
			{
				nums[i*j] = false;
			}
		}
	}
	for (int i = 2; i < nums.size(); i++)
	{
		if (nums[i])
		{
			primes.push_back(i);
		}
	}
	return primes;
}

int main(void)
{
	int n;
	std::cin >> n;
	std::vector<int> primes = sieve(n);
	std::vector<int> dp(n + 1, 0);
	for (auto p: primes)
	{
		for (int i = n; i  >= p+2; i--)
		{
			int ref = i - p;
			if (dp[ref] && dp[ref] >= dp[i])
			{
				dp[i ] = dp[ref] + 1;
			}
		}
		if (!dp[p])
		{
			dp[p] = 1;
		}
	}
	if (dp[n])
	{
		std::cout << dp[n] << std::endl;
	}
	else
	{
		std::cout << -1 << std::endl;
	}
	system("pause");
	return 0;
}