#include <stdio.h>
#include <math.h>
#include <limits.h>

int snt(int a, int arr[], int max) {
	int i;

	for (i = 1; i <= max; i++) {
		if (a == arr[i]) {
			return 1;
		}
	}

	return 0;
}

int findMax(int a, int b) {
	return a > b ? a : b;
}

int f[20000][30000] = {};
const int inf = -INT_MAX;

int main() {
	int n;
	int i, j;
	int max;
	int check[21000] = {};
	int arr[20000] = {};


	scanf("%d", &n);

	for (i = 2; i <= sqrt(n); i++) {
		for (j = 2; j <= n / i; j++) {
			check[i*j] = 1;
		}
	}

	max = 1;
	for (i = 2; i <= n; i++) {
		if (!check[i]) arr[max++] = i;
	}
	max--;

	for (i = 1; i <= n; i++) {
		f[0][i] = inf;
	}

	for (i = 1; i <= max; i++) {
		for (j = 0; j <= n; j++) {
			if (j - arr[i] >= 0) {
				f[i][j] = findMax(f[i - 1][j], f[i - 1][j - arr[i]] + 1);
			}
			else {
				f[i][j] = f[i - 1][j];
			}
		}
	}


	int result = (f[max][n] <0 ? -1 : f[max][n]);
	printf("%d", result);
	getchar(); getchar();

	return 0;
}