#!/usr/bin/python
# -*- coding: utf-8 -*-
N, K = map(int, raw_input().split())
S = list(raw_input())
S = map(int, S)
pay_1 = []
pay_2 = []
free = 0

for n in xrange(N):
    s = S[n]
    if free == 0:
        pay_1.append(1)
    else:
        pay_1.append(0)
        free -= 1
    
    if s != 0:
        free += s
    if n+1 == K:
        print sum(pay_1)
        exit()

for n in xrange(N):
    s = S[n]
    if free == 0:
        pay_2.append(1)
    else:
        pay_2.append(0)
        free -= 1
    
    if s != 0:
        free += s
    if N + n + 1 == K:
        print sum(pay_1) + sum(pay_2)
        exit()

if sum(pay_2) == 0: #全部0だと無限パターン
    print sum(pay_1) 
    exit()
else:
    pay = sum(pay_1)
    K -= N
    pay += sum(pay_2) * (K / N)
    K = K%N
    if K == 0:
        print pay
        exit()
    pay_3 = []
    for n in xrange(N):
        s = S[n]
        if free == 0:
            pay_3.append(1)
        else:
            pay_3.append(0)
            free -= 1
    
        if s != 0:
            free += s
        if n+1 == K:
            print pay + sum(pay_3) 
#ぐちゃぐちゃになった