#!/usr/bin/env python3
# %%
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines


# %%
import itertools

# %%
N, K = map(int, readline().split())
S = [int(x) - ord('0') for x in read().rstrip()]

# %%


def get_init_counts():
    """ある箱に挑むときにもっているタダ券の枚数"""
    yield 0
    have = 0
    for i in range(100):
        for j in range(N):
            if not have:
                have += S[j]
            else:
                have += S[j] - 1
        yield have


# %%
def find_period(seq):
    for i in itertools.count(1):
        if seq[i] == seq[i + i]:
            return i


def final_simulate(n, k):
    have = n
    buy = 0
    for j in range(k):
        if not have:
            buy += 1
            have += S[j]
        else:
            have += S[j] - 1
    return buy


# %%
def solve(K):
    cnts = list(get_init_counts())
    if K <= 100 * N:
        q, r = divmod(K, N)
        n = cnts[q]
        free_get = sum(S) * q - n
        return N * q - free_get + final_simulate(n, r)
    if cnts[-1] >= 90:
        return solve(100 * N)
    p = find_period(cnts)
    q, r = divmod(K, N)
    n = cnts[q % p + p]
    free_get = sum(S) * q - n
    return N * q - free_get + final_simulate(n, r)


# %%
print(solve(K))