N = int(input())
prime = []
for i in range(2,N+1):
	j = 2
	flag = False
	while j * j <= i:
		if i % j == 0:
			flag = True
			break
		j+=1
	if not flag:
		prime.append(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)