yuki_458.py

# ------------------------------------
# yukicoder
# No.458 異なる素数の和
# http://yukicoder.me/problems/no/458
# ------------------------------------


from math import sqrt, ceil
N = int(input())

def era_prime(N):
	temp = [True for _ in range(N+1)]
	temp[0] = temp[1] = False
	key = ceil(sqrt(N+1))
	for i in range(2, key):
		if temp[i]:
			for k in range(i+i, N+1, i):
				temp[k] = False
	primes = [index for index, is_prime in enumerate(temp) if is_prime]
	return primes


primes = era_prime(N)


data = dict()
keys = list()
for prime in primes:
	if prime > 480: break
	new_keys = list()
	for key in [x for x in keys if x+prime < N + 1][::-1]:
		if key+prime not in data:
			data[key+prime] = data[key] + 1
			new_keys.append(key+prime)
		else:
			data[key+prime] = max(data[key+prime], data[key]+1)
	if prime not in data:
		data[prime] = 1
		new_keys.append(prime)

	keys += new_keys

if N in data:
	print(data[N])
else:
	print(-1)