import sys; input = sys.stdin.buffer.readline
sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

num = 2 * 10 ** 4 + 1 #適当に値を入れる
L = [1 for i in range(num)]; L[0] = 0; L[1] = 0
plist = []
for i in range(num):
	if L[i] == 1:
		plist.append(i); c = 2
		while i * c <= num - 1:
			L[i * c] = 0; c += 1

#処理内容
def main():
	N = int(input())
	DP = [0] * (N + 1)
	DP[0] = 1
	for i in plist:
		for j in range(N, -1, -1):
			if j + i <= N and DP[j] != 0:
				DP[i + j] = max(DP[i + j], DP[j] + 1)

	# print(DP)
	if DP[N] == 2 or DP[N] == 0:
		print(-1)
	else:
		print(DP[N] - 1)

if __name__ == '__main__':
	main()