def main():
    n, k = [int(x) for x in input().split(" ")]
    s = list(input())
    l = []

    for i in range(len(s)):
        if i > k and len(l) == k:
            ans = i
            break

        if s[i] == "(":
            l.append(s[i])
        else:
            l.pop()

    print(ans)


if __name__ == "__main__":
    main()