def primes2(limit):
    ''' returns a list of prime numbers upto limit.
    source: Rossetta code: Sieve of Eratosthenes
    http://rosettacode.org/wiki/Sieve_of_Eratosthenes#Odds-only_version_of_the_array_sieve_above
    '''
    if limit < 2: return []
    if limit < 3: return [2]
    lmtbf = (limit - 3) // 2
    buf = [True] * (lmtbf + 1)
    for i in range((int(limit ** 0.5) - 3) // 2 + 1):
        if buf[i]:
            p = i + i + 3
            s = p * (i + 1) + i
            buf[s::p] = [False] * ((lmtbf - s) // p + 1)
    return [2] + [i + i + 3 for i, v in enumerate(buf) if v]

def solve(N):
    primes = primes2(N)
    dp = [-1] * (N + 1)
    dp[0] = 0
    for p in primes:
        for i in range(N, p - 1, -1):
            if dp[i - p] != -1:
                dp[i] = max(dp[i], dp[i - p] + 1)
    return dp[N]

N = int(input())
print(solve(N))