N, A = (int(x) for x in input().split())
S = input()

result = 0
r = 1200
nr = r
count = 0
for i in range(N):
    if S[i] == '0':
        nr -= 1
    elif nr < 1200:
        nr += 1
        count += 1
    if count == A:
        print(i + 1)
        exit()

result += N
A -= count

while True:
    nnr = nr
    ncount = 0
    for i in range(N):
        if S[i] == '0':
            nnr -= 1
        elif nnr < 1200:
            nnr += 1
            ncount += 1
        if ncount == A:
            print(result + i + 1)
            exit()

    result += N
    A -= ncount

    if nnr - nr != nr - r:
        r = nr
        nr = nnr
        continue

    result += ((A - 1) // ncount) * N
    A %= ncount
    if A == 0:
        A = ncount
    count = 0
    for i in range(N):
        if S[i] == '0':
            nnr -= 1
        elif nnr < 1200:
            nnr += 1
            count += 1
        if count == A:
            print(result + i + 1)
            exit()