import math


def is_prime(n):
    if n == 1:
        return False
    for t in range(2, math.ceil(math.sqrt(n)) + 1):
        if n % t == 0:
            return False
    return True


def find(string_num, s):
    if not is_prime(int(string_num)):
        return s
    s += 1
    out = [s]
    for x in range(len(string_num)):
        w = string_num[:x] + string_num[x + 1:]
        if not w:
            continue
        w = str(int(w))

        out.append(find(w, s))
    return max(out)


it = input()

print(find(it, 0))