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