"""

https://yukicoder.me/problems/no/3266

1周で1200に戻る場合 -> 1周目が永続
戻らない場合 -> 2周目が永続

"""

import sys

N,A = map(int,input().split())
S = input()

R = 1200
lp1 = 0
for i in range(N):
    if S[i] == "0":
        R -= 1
    elif R < 1200:
        R += 1
        lp1 += 1

# 1周で戻る場合
if R == 1200:
    ans = ( (A-1) // lp1) * N
    now = ( (A-1) // lp1) * lp1
    for i in range(N):
        ans += 1
        if S[i] == "0":
            R -= 1
        elif R < 1200:
            R += 1
            now += 1

        if now == A:
            break
    print (ans)
    sys.exit()


lp2 = 0
for i in range(N):
    if S[i] == "0":
        R -= 1
    elif R < 1200:
        R += 1
        lp2 += 1

# print (lp1,lp2)

ans = N + ( (A-lp1-1)//lp2) * N
now = lp1 + ( (A-lp1-1)//lp2) *lp2
for i in range(N):
    ans += 1
    if S[i] == "0":
        R -= 1
    elif R < 1200:
        R += 1
        now += 1

    if now == A:
        break
print (ans)