#include <iostream>
#include <string>
#include <vector>
#include <climits>
using namespace std ;
const int MAXCOST = 1200 ;
int counts[MAXCOST] ;
void check(string &s, int &mindep, int &finaldep) {
   int dep = 0 ;
   mindep = 0 ;
   for (int i=0; i<s.size(); i++)
      if (s[i] == '(') {
         dep++ ;
      } else {
         mindep = min(mindep, --dep) ;
      }
   finaldep = dep ;
}
int main(int argc, char *argv[]) {
   int n, k ;
   string s ;
   cin >> n >> k >> s ;
   vector<int> c(n) ;
   int basevalue = 0 ;
   for (int i=0; i<n; i++) {
      cin >> c[i] ;
      if (c[i] < 0) {
         c[i] = - c[i] ;
         basevalue += c[i] ;
         s[i] = '(' + ')' - s[i] ;
      }
   }
   int mindep, finaldep ;
   check(s, mindep, finaldep) ;
   int leftfix = (1-mindep) >> 1 ;
   int rightfix = (1+finaldep-mindep) >> 1 ;
   int fixcost = leftfix + rightfix ;
   if (fixcost > k || (n & 1)) {
      cout << (-basevalue) << endl ;
      exit(0) ;
   }
   int avail = 0 ;
   for (int i=0; i<n; i++)
      if (s[i] == ')') {
         counts[c[i]]++ ;
         avail++ ;
      }
   int bestsol = INT_MAX ;
   int dep = 0 ;
   for (int i=0; i<=n; i++) {
      int leftfix = (1-dep) >> 1 ;
      int 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]) {
               if (counts[ci] >= need) {
                  totcost += ci * need ;
                  break ;
               } else {
                  totcost += ci * counts[ci] ;
                  need -= counts[ci] ;
               }
            }
         }
         bestsol = min(bestsol, totcost) ;
      }
      if (i < n) {
         if (s[i] == ')') {
            dep-- ;
            counts[c[i]]-- ;
            avail-- ;
         } else {
            dep++ ;
            counts[c[i]]++ ;
            avail++ ;
         }
      }
   }
   if (bestsol == INT_MAX)
      cout << "?" << endl ;
   else
      cout << (bestsol - basevalue) << endl ;
}