import math

def sieve(n):
    ass = []
    is_prime = [True]*(n+1)
    is_prime[0] = False
    is_prime[1] = False

    for i in range(2, int(math.sqrt(n))+1):
        if not is_prime[i]:
            continue
        for j in range(i*2, n+1, i):
            is_prime[j] = False
    for i in range(n+1):
        if is_prime[i]:
            ass.append(i)
    return(ass)

def main():

    n = int(input())
    P = sieve(n)
    dp = [-1]*(n+1)
    dp[0] = 0
    for p in P:
        for i in reversed(range(n+1)):
            if dp[i] == -1:
                continue
            if i+p <= n:
                dp[i+p] = max(dp[i+p], dp[i]+1)

    print(dp[n])

if __name__ == '__main__':
    main()