#include <iostream>
#include <string>

using namespace std;

int main()
{
    int n, k, m=0 ,ans=0;
    string s;
    cin >> n >> k;
    cin >> s;
    for(int i = 0; i < k; i++)m += ( s[i] == '(' ) ? 1 : -1;
    k--;
    if(s[0] == '(' && s[k] == ')' && m == 0)ans++;
    for(int i = 1; i < n-k; i++){
        m += ( s[i-1] == '(' ) ? -1 : 1;
        m += ( s[i+k] == ')' ) ? -1 : 1;
        if(s[i] == ')') continue;
        if(s[i+k] == '(') continue;
        if(m)continue;
        ans++;
        };
    cout << ans;
    return 0;
}