// Java version of tgr's cpp solution by font
// (my autojudge script is Java only)

import java.util.*;
import java.io.*;

public class unb_tgr_port
{
   public static void main(String[] args) throws Exception
   {
      PrintWriter out = new PrintWriter(System.out);
      new unb_tgr_port(new FastScanner(System.in), out);
      out.close();
   }

   public unb_tgr_port(FastScanner in, PrintWriter out)
   {
      int n = in.nextInt();
      int k = in.nextInt();
      String s = in.next();
      int[] c = new int[n];
      int basevalue = 0;
      StringBuilder sb = new StringBuilder();
      for (int i=0; i<n; i++)
      {
         c[i] = in.nextInt();   
         if (c[i] < 0)
         {
            c[i] = -c[i];
            basevalue += c[i];
            sb.append(s.charAt(i) == '(' ? ')' : '(');
         }
         else
         {
            sb.append(s.charAt(i));
         }
      }
      s = sb.toString();
  
      int mindep, finaldep;
      int dep = 0;
      mindep = 0;
      for (int i=0; i<s.length(); i++)
      {
         if (s.charAt(i) == '(')
            dep++;
         else
         {
            dep--;
            mindep = Math.min(mindep, dep);
         }
      }
      finaldep = dep;

      int leftfix = (1-mindep) >> 1;
      int rightfix = (1+finaldep-mindep) >> 1;
      int fixcost = leftfix + rightfix;
      if (fixcost > k || n%2 == 1)
      {
         out.println(-basevalue);
         return;
      }

      int MAXCOST = 1200;
      int[] counts = new int[MAXCOST];
      int avail = 0;
      for (int i=0; i<n; i++)
         if (s.charAt(i) == ')') {
            counts[c[i]]++;
            avail++;
         }
  
      int bestsol = Integer.MAX_VALUE;
      dep = 0;
      for (int i=0; i<=n; i++)
      {
         leftfix = (1-dep) >> 1;
         rightfix = (1+finaldep-dep) >> 1;
         if (avail + leftfix + rightfix > k)
         {
            int totcost = 0;
            int need = k - leftfix - rightfix + 1;
            for (int ci=0; need > 0; ci++)
            {
               if (counts[ci] > 0)
               {
                  if (counts[ci] >= need)
                  {
                     totcost += ci * need;
                     break;
                  }
                  else
                  {
                     totcost += ci * counts[ci];
                     need -= counts[ci];
                  }
               }
            }
            bestsol = Math.min(bestsol, totcost);
         }

         if (i < n)
         {
            if (s.charAt(i) == ')')
            {
               dep--;
               counts[c[i]]--;
               avail--;
            }
            else
            {
               dep++;
               counts[c[i]]++;
               avail++;
            }
         }
      }

      if (bestsol == Integer.MAX_VALUE)
         out.println("?");
      else
         out.println(bestsol - basevalue);
   }
}

class FastScanner{
    private InputStream stream;
    private byte[] buf = new byte[1024];
    private int curChar;
    private int numChars;
    
    public FastScanner(InputStream stream)
    {
        this.stream = stream;
    }
    
    int read()
    {
        if (numChars == -1)
            throw new InputMismatchException();
        if (curChar >= numChars){
            curChar = 0;
            try{
                numChars = stream.read(buf);
            } catch (IOException e) {
                throw new InputMismatchException();
            }
            if (numChars <= 0)
                return -1;
        }
        return buf[curChar++];
    }
    
    boolean isSpaceChar(int c)
    {
        return c==' '||c=='\n'||c=='\r'||c=='\t'||c==-1;
    }
    
    boolean isEndline(int c)
    {
        return c=='\n'||c=='\r'||c==-1;
    }
    
    int nextInt()
    {
        return Integer.parseInt(next());
    }
    
    long nextLong()
    {
        return Long.parseLong(next());
    }
    
    double nextDouble()
    {
        return Double.parseDouble(next());
    }
    
    String next(){
        int c = read();
        while (isSpaceChar(c))
            c = read();
        StringBuilder res = new StringBuilder();
        do{
            res.appendCodePoint(c);
            c = read();
        }while(!isSpaceChar(c));
        return res.toString();
    }
    
    String nextLine(){
        int c = read();
        while (isEndline(c))
            c = read();
        StringBuilder res = new StringBuilder();
        do{
            res.appendCodePoint(c);
            c = read();
        }while(!isEndline(c));
        return res.toString();
    }
}