N = int(input())
is_prime = [True for i in range(N+1)]
is_prime[0] = is_prime[1] = False
for i in range(2,N+1):
	if not is_prime[i]:
		continue
	for j in range(i*2,N+1,i):
		is_prime[j] = False
prime = [i for i in range(2,N+1) if is_prime[i]]
P = len(prime)
dp = [0 for i in range(N+1)]
dp[0] = 1
for i in range(P):
	for j in range(N,-1,-1):
		if dp[j] and j+prime[i] <= N:
			dp[j+prime[i]] = max(dp[j+prime[i]],dp[j]+1)
print(dp[N]-1 if dp[N] != 0 else -1)