n, k = map(int, input().split())
s = list(input())

l = k-1
p = 1 if s[k-1] == "(" else -1

c = 0
while l >= 0:
    if s[l] == '(':
        c += p
    else:
        c -= p

    if c <= 0:
        break
    l += p

print(l + 1)