n = int(input())

IsPrime = [True for _ in range(n + 1)]
IsPrime[0] = IsPrime[1] = False
Primes = []
for i in range(2, n + 1):
    if IsPrime[i]:
        Primes.append(i)
        for j in range(i * i, n + 1, i):
            IsPrime[j] = False

DP = [-1 for _ in range(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)
print(DP[n])