# 20000以下の素数を用いたナップサック

N = int(input())
F = [True] * (N + 1)

F[0] = False
F[1] = False
facts = []
for i in range(2, N + 1):
    if F[i]:
        facts.append(i)
        for j in range(i * i, N + 1, i):
            F[j] = False

dp = [-1] * (N + 1)
dp[0] = 0
for f in facts:
    for i in range(N, -1, -1):
        if dp[i] == -1:
            continue
        if i + f > N:
            continue
        dp[i + f] = max(dp[i + f], dp[i] + 1)
        
print(dp[N])