N,K = [int(i) for i in input().split()]
S = list(input())
buy = 1
eat = 1
atari = int(S[0])
box = 1
while eat < K:
    if atari >= 1:
        atari += int(S[box])
        box += 1
        eat+= 1
        atari -= 1
    elif atari == 0:
        atari += int(S[box])
        eat += 1
        buy += 1
        box += 1
    if box >= N:
        box -= N
print(buy)