n = int(input())
s = [1]*(n+1)
p = 2
while p*p <= n:
    if s[p]:
        for i in range(p*2, n+1, p):
            s[i] = 0
    p += 1

_ = range(n+1)
__ = [0]+[-1]*n
dp = [__*1]
add = dp.append
i = 0

for k in range(2, n+1):
    if s[k]:
        add(__*1)
        for w in _:
            dp[i][w] = max(1+dp[i-1][w-k], dp[i-1][w]) if k <= w and dp[i-1][w-k] != -1 else dp[i-1][w]
        i += 1

print(dp[i-1][n])