# -*- coding: utf-8 -*-

N, K = map(int, raw_input().split())
S = raw_input()


def check_set(S):
    stock = 0
    buy = 0
    for c in S:
        if stock > 0:
            stock -= 1
        else:
            buy += 1
        stock += int(c)
    return buy, stock


if N >= K:
    buy, stock = check_set(S[:K])
    print buy
else:
    buy, stock = check_set(S)
    if stock >= buy:
        print buy
    else:
        adjust = (N + ((N % K) - 1)) % N + 1
        buy2, stock2 = check_set(S[:adjust])
        print buy + ((K - N) // N) * (buy2 - stock2)