Envío 2191

Código

def max_substr(s, k):
    i = 0
    n = len(s)
    curr_max = 0
    letters = dict()

    for j in range(n):
        l = s[j]
        cl = letters.get(l, 0)
        letters[l] = cl + 1

        while len(letters.items()) > k:
            l = s[i]
            cl = letters.get(l, 1)
            letters[l] = cl - 1

            if letters[l] == 0:
                del letters[l]
            i = i + 1

        curr_max = max(curr_max, j - i + 1)

    return curr_max

s = input()
k = int(input())
print(max_substr(s,k ))