def primes(n):
    is_p = [True for i in range(n+1)]
    i = 2
    while i * i <= n:
        if is_p[i]:
            for j in range(i*i,n+1,i):
                is_p[j] = False
        i += 1
    return [i for i in range(2,n+1) if is_p[i]]

n = int(input())
p = primes(n)
mp = {0:0}
for i in range(len(p)):
    tmp = {}
    for x in mp:
        if x + p[i] > n: break
        tmp[x+p[i]] = max(mp[x]+1,mp[x+p[i]] if x+p[i] in mp else -1)
    mp.update(tmp)
print(mp[n] if n in mp else -1)