N,K = map(int,input().split())
S = input()
count = 0
count_pos = 0
if S[K-1] == "(":
    for i in range(K,N):
        if S[i-1] == "(":
            count += 1
        if S[i-1] == ")":
            count -= 1
        if count == 0:
            count_pos = i
            break
if S[K-1] == ")":
    S = S[::-1]
    for i in range(K,N-K):
        if S[i] == ")":
            count += 1
        if S[i] == "(":
            count -= 1
        if count == 0:
            count_pos = i
            break
print(count_pos)