# coding: utf-8

def readint():
    return int(input())

def readints():
    return list(map(int, input().split()))

def sieve(n):
    primes = [2] if n >= 2 else []
    used = [False] * (n + 1)
    for i in range(3, n + 1, 2):
        if not used[i]:
            primes.append(i)
            for j in range(i + i, n + 1, i):
                used[j] = True
    return primes

def main():
    n = readint()

    primes = sieve(n)
    # print("primes", len(primes))
    dp = [0] * (n + 1)
    upper = 0
    for p in primes:
        for i in range(upper, 0, -1):
            if i + p <= n and dp[i] > 0:
                dp[i + p] = max(dp[i + p], dp[i] + 1)
                upper = max(upper, i + p)
        dp[p] = max(dp[p], 1)
        upper = max(upper, p)

    ans = dp[n]
    if ans >= 1:
        print(ans)
    else:
        print(-1)

if __name__ == "__main__":
    main()