#include<bits/stdc++.h>
//#include<atcoder/all>
//using namespace atcoder;
using namespace std;
using ll = long long;

int main(){
	int n,k;
	cin >> n >> k;
	string s;
	cin >> s;
	int l =0 ;
	for(int i = 0;i<k;i++){
		if(s[i]=='(')l++;
		else l--;
	}
	reverse(s.begin(),s.end());
	for(int i  =0;i<n;i++){
		if(s[i]==')')l--;
		else l++;
		if(l==0){
			cout<<n-i<<endl;
			return 0;
		}
	}
	cout<<l<<endl;
}