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

    for i in range(len(s) - 1):
        if i + 1 > k and len(l) == k:
            ans = i + 1

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

    print(ans)

if __name__ == "__main__":
    main()