def primes(n):
    is_p = [True for i in range(n+1)]
    i = 2
    while i * i <= n:
        if is_p[i]:
            for j in range(i*i,n+1,i):
                is_p[j] = False
        i += 1
    return [i for i in range(2,n+1) if is_p[i]]

n = int(input())
p = primes(n)
dp = [-1] * (n+1)
dp[0] = 0
for i in range(len(p)):
    for j in range(n,p[i]-1,-1):
        if dp[j-p[i]] >= 0:
            dp[j] = max(dp[j],dp[j-p[i]]+1)
print(dp[n])