import sys

input = sys.stdin.readline


def main():
    N, K = map(int, input().split())
    S = []
    for i, s in enumerate(input().rstrip()):
        if s == '(':
            S.append(i)
        else:
            a = S.pop()
            if 1+a == K or 1+i == K:
                print(a+i+2-K)
                return


if __name__ == '__main__':
    main()