N, K = map(int, input().split())
S = [int(s) for s in input()]
ans, x, y = 0, 0, 0
for i in range(N):
    if y:
        y -= 1
    else:
        x += 1
    y += S[i]
    if i == K - 1:
        print(x)
        exit()
if y >= x:
    print(x)
    exit()
    
K -= N
ans = x + (x - y) * ((K - 1)//N)
K -= (K - 1)//N*N
for i in range(N):
    if y:
        y -= 1
    else:
        ans += 1
    y += S[i]
    if i == K - 1:
        print(ans)
        exit()