N, K = map(int, input().split())

s = list(input())

i = K - 1
p = 1 if s[i] == '(' else -1

count = 0
while(0 <= i < N):
    if s[i] == '(':
        count += p
    else:
        count -= p
    if count <= 0:
        break
    i += p

print(i + 1)