from math import sqrt, ceil

def Sieve(n):
    lst = [True] * (n + 1)
    S = set()
    for i in range(2, ceil(sqrt(n)) + 1):
        if lst[i]:
            for j in range(2 * i, n + 1, i):
                lst[j] = False
    for i in range(2, n + 1):
        if lst[i]:
            S.add(i)
    return sorted(list(S))

N = int(input())
P = Sieve(N + 100)
M = len(P)
inf = 10 ** 18
pre = [-inf] * (N + 1)
pre[0] = 0
for i in range(M):
    dp = [-inf] * (N + 1)
    for j in range(N + 1):
        dp[j] = pre[j]
        if j - P[i] < 0:
            continue
        dp[j] = max(dp[j], pre[j - P[i]] + 1)
    dp, pre = pre, dp

print(pre[-1]) if pre[-1] > 0 else print(-1)