def checker(s, x, f):
  i = 1 if f else -1
  chk = ")" if f else "("
  a = [x]
  while (True):
    x += i
    if x < 1 or x > len(s):
      break
    if s[x - 1] == chk:
      if len(a) == 1:
        return x
      else:
        a.pop()
    else:
      a.append(x)
  return -1
n, k = map(int, input().split())
s = input()
print(checker(s, k, s[k - 1] == "("))