def check(K):
    ret = 0
    cnt = 0
    for i in range(K):
        if cnt == 0:
            ret += 1
        else:
            cnt -= 1
        cnt += S[i]
    return cnt, ret

N,K = map(int,input().split())
S = list(map(int,input()))
if K <= N:
    _,ans = check(K)
    print(ans)
else:
    cnt,buy = check(N)
    if buy < cnt:
        print(buy)
    else:
        _,ans = check(max(0, K%N-cnt))
        print(buy + (buy-cnt) * (K//N-1) + ans)