N = 200000
isprime = [True] * N
isprime[0] = isprime[1] = False
for i in range(2, int(N ** 0.5 + 1)):
    if not isprime[i]:
        continue
    for j in range(i * i, N, i):
        isprime[j] = False

n = int(input())
dp = [-1 << 30] * (n + 1)
dp[0] = 0
primes = [i for i, tf in enumerate(isprime[:n + 1]) if tf]
for p in primes:
    for i in range(n, p - 1, -1):
        dp[i] = max(dp[i], dp[i - p] + 1)
if dp[n] < 0:
    dp[n] = -1
print(dp[n])