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

def f(r):
    cnt = 0
    include_do_nothing = False
    for c in S:
        if c == "0":
            r -= 1
        elif r <= 1199:
            r += 1
            cnt += 1
        else:
            include_do_nothing = True
    return r, cnt, include_do_nothing

def g(r, t):
    t += 1
    cnt = 0
    for i, c in enumerate(S):
        if c == "0":
            r -= 1
        elif r <= 1199:
            r += 1
            t -= 1
            if t == 0:
                return i
    return -1

A -= 1

r = 1200
loop = 0
while True:
    # print(loop, r, A)
    rr, cnt, flag = f(r)
    if cnt >= A or r == rr or not flag:
        loop += A // cnt
        A %= cnt
        print(loop * N + g(r, A) + 1)
        break

    r = rr
    A -= cnt
    loop += 1