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

nn = range(n+1)
dp = [[0]+[-1]*n for j in nn]
i = 0
for k in range(2, n+1):
    if s[k]:
        for w in nn:
            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])