#coding:utf-8

N,K=map(int,raw_input().split())
S=raw_input()

cnt,ans=0,0

if S[K-1] == '(':	
	for i in S[K-1:]:
		cnt+=1
		if i == '(':
			ans+=1
		else:
			ans-=1
			if ans == 0:
				print cnt+(K-1)
				break
else:
	for i in S[:K][::-1]:
		cnt+=1
		if i == ')':
			ans+=1
		else:
			ans-=1
			if ans == 0:
				print cnt-(K-1)
				break