using System;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        int[] NK = Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray();
        char[] S = Console.ReadLine().ToArray();

        int kakko = 0;
        int idx = 0;

        if ('('.Equals(S[NK[1] - 1]))
        {
            for (idx = NK[1]; idx < S.Length; idx++)
            {
                if (kakko < 0) break;
                if ('('.Equals(S[idx])) kakko++;
                if (')'.Equals(S[idx])) kakko--;
            }
        }
        else
        {
            for (idx = NK[1] - 2; 0 < idx; idx--)
            {
                if (kakko < 0) break;
                if (')'.Equals(S[idx])) kakko++;
                if ('('.Equals(S[idx])) kakko--;
            }
            idx =- 1;
        }
        Console.WriteLine(idx);
    }
}