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

a,b = 0,0
for i in range(min(N,K)):
    if b:
        b -= 1
    else:
        a += 1
    b += int(S[i])
if K<=N:
    print(a)
    exit()

if b>=a:
    print(a)
else:
    c,d = K//N,K%N
    e = (a-b)*(c-1)
    res = a+e
    a = 0
    for i in range(d):
        if b:
            b -= 1
        else:
            a += 1
        b += int(S[i])
    print(res+a)