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

N, K = map(int, raw_input().split())
S = raw_input()
stock = 0
buy = 0
for c in S:
    if stock > 0:
        stock -= 1
    else:
        buy += 1
    a = int(c)
    stock += int(c)

if buy <= stock:
    # もう買う必要がない
    print buy
else:
    print buy + ((K - buy) // N) * (buy - stock)