n, k = map(int, input().split())
S = list(map(int, input()))
cnt = 0
tot = 0
for i, s in enumerate(S, 1):
    if tot == 0:
        cnt += 1
        tot += 1
    tot -= 1
    tot += s
    if i == k:
        print(cnt)
        exit()
    
if sum(S) > n:
    print(cnt)
    exit()
c = (k - 1) // n - 1
cnt += c * (n - sum(S))
k = (k - 1) % n + 1

for i, s in enumerate(S, 1):
    if tot == 0:
        cnt += 1
        tot += 1
    tot -= 1
    tot += s
    if i == k:
        print(cnt)
        exit()