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

    ans = 0

    x1 = 0
    y1 = 0

    b1, b2 = divmod(K, N)

    if b1 > 0:
        for i in range(N):
            if y1 == 0:
                x1 += 1
            else:
                y1 -= 1
            y1 += S[i]
        x2 = max(x1 - y1, 0)
        ans += x1
        b1 -= 1
        ans += b1 * x2

    x3 = 0
    y3 = y1
    for i in range(b2):
        if y3 == 0:
            x3 += 1
        else:
            y3 -= 1
        y3 += S[i]

    ans += x3

    print(ans)


if __name__ == '__main__':
    solve()