file = [i.rstrip() for i in open("input").readlines()]

import hashlib

key = file[0]
i = 1
while True:
    output = hashlib.md5("{}{}".format(key, str(i)).encode())
    digest = output.hexdigest()
    # change from [0:6] to [0:5] for sol 1
    if len(set(digest[0:6])) == 1 and digest[0] == '0':
        # we've 'mined' a coin
        print(i)
        break

    i += 1