n = int(input())

prime = []
is_prime = [False] * 2 + [True] * (n - 1)
def get_val():
    for i in range(2,n+1):
        if is_prime[i]:
            prime.append(i)
            for j in range(i * i, n + 1, i):
                is_prime[i] = False
    

get_val()

dp = [0] + [-1] * n
for x in prime:
    for i in range(n,x,-1):
        if dp[i-x] == -1: continue
        dp[i] = max(dp[i], dp[i-x] + 1)
print(dp[n])