import sys


def input(): return sys.stdin.readline().rstrip()


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

    s = sum(map(int, S))
    if s >= N:
        K = min(N, 50)

    rep = max(0, (K - 100 * N) // N)
    ans = rep * (N - s)
    K -= N * rep

    cur = 0
    for i in range(K):
        if cur == 0:
            ans += 1
        else:
            cur -= 1
        cur += int(S[i % N])

    print(ans)


if __name__ == '__main__':
    main()