#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cmath>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
typedef long long lint;

#define MIN(a,b) ((a)<(b)?(a):(b))
#define MAX(a,b) ((a)>(b)?(a):(b))

int main()
{
	int i, N, K, scope = 0, l;
	string S; 

	cin >> N >> K >> S;

	for (i = 0; i < K; i++)
		S[i] == '(' ? scope++ : scope--;
	l = scope;

	for (; scope != l - 1; i++)
		S[i] == '(' ? scope++ : scope--;
	
	cout << i << endl;

	return 0;
}