// yukicoder: No.458 異なる素数の和
// 2019.4.23 bal4u

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

#define MAX  20000
#define SQRT 141	     // sqrt(MAX)
char prime[MAX+2] = {1,1,0,0,1,0,1,0,1,1,0};       // 0:素数
int tbl[2300], sz;       // sz=2262

int a[MAX+2];
int b[MAX+2];

void sieve(int n)
{
	int i, j, b;
	b = (int)sqrt((double)n);
	for (i = 3; i <= b; i += 2) {
		for (j = i*i; j <= n; j += i) prime[j] = 1;
	}
	tbl[0] = 2, sz = 1;
	for (i = 3; i <= MAX; i+=2) if (!prime[i]) tbl[sz++] = i;
}

int main()
{
	int i, j, N;

	scanf("%d", &N);
	sieve(N);
	a[N] = 1;
	memset(b, -1, sizeof(b));
	for (i = N; i >= 0; i--) if (a[i]) {
		for (j = b[i]+1; j < sz; j++) {
			if (i-tbl[j] >= 0) a[i-tbl[j]] = a[i]+1, b[i-tbl[j]] = j;
		}
	}
	if (a[0] == 0) puts("-1");
	else printf("%d\n", a[0]-1);
	return 0;
}