package yukicoder;

import java.util.*;

public class Q458 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		boolean[] isPrime = new boolean[N + 1];
		Arrays.fill(isPrime, true);
		isPrime[0] = isPrime[1] = false;
		for (int i = 2; i <= N; ++i) {
			if (isPrime[i]) {
				for (int j = 2 * i; j <= N; j += i) {
					isPrime[j] = false;
				}
			}
		}

		ArrayList<Integer> prime = new ArrayList<>();
		for (int i = 2; i <= N; ++i) {
			if (isPrime[i])
				prime.add(i);
		}

		int[] dp = new int[N + 1];

		for (int p : prime) {
			for (int i = N; i >= 0; --i) {
				if (p + i <= N && (dp[i] > 0 || i == 0)) {
					dp[p + i] = Math.max(dp[i] + 1, dp[p + i]);
				}
			}
		}
		if (dp[N] > 0)
			System.out.println(dp[N]);
		else
			System.out.println("-1");
	}
}