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

MAX = 0
cnt = 0
for s in S:
    if s == "0":
        cnt -= 1
    else:
        cnt += 1
    MAX = max(MAX, cnt)
limit = 1200-MAX

cnt1 = S.count("1")
visited = set()
rate = 1200
now = 0
ans = 0
counter = 0
while rate not in visited:
    visited.add(rate)
    c = max(rate-limit, 0)
    if A <= now+(cnt1-c):
        break
    ans += N
    now += cnt1-c
    rate += cnt1-(N-cnt1)-c
    counter += 1
    if counter == 10**5*5:
        break
if rate in visited:
    c = max(rate-limit, 0)
    cnt = (A-now-1)//(cnt1-c)
    ans += N*cnt
    now += (cnt1-c)*cnt
    rate += (cnt1-(N-cnt1)-c)*cnt
elif now+(cnt1-c) < A:
    cnt = (A-now-1)//cnt1
    ans += N*cnt
    now += cnt1*cnt
    rate += (cnt1-(N-cnt1))*cnt

for s in S:
    ans += 1
    if s == "0":
        rate -= 1
    else:
        if rate < 1200:
            rate += 1
            now += 1
    if now == A:
        print(ans)
        break