def main():
    N = int(input())
    import math
    def sieve_of_eratosthenes(n):
        prime = [True]*(n+1)
        prime[0] = False
        prime[1] = False

        sqrt_n = math.ceil(math.sqrt(n))
        for i in range(2, sqrt_n+1):
            if prime[i]:
                for j in range(2*i, n+1, i):
                    prime[j] = False
        prime = [i for i in range(2, n + 1) if prime[i]]
        return prime

    num = sieve_of_eratosthenes(N)
    dp = [[-1]*(N+1) for _ in range(len(num))]
    dp[0][2] = 1
    for i in range(1, len(num)):
        for j in range(2, N-num[i]+1):
            if dp[i-1][j] > 0:
                dp[i][j] = dp[i-1][j]
            if j + num[i] <= N and dp[i-1][j] > 0:
                dp[i][j+num[i]] = max(dp[i][j+num[i]], dp[i-1][j]+1)
    ans = -1
    for i in range(len(num)):
        ans = max(ans, dp[i][N])
    print(ans)
if __name__ == '__main__':
    main()