import java.util.*;
public class SayThePhotos
{
public static void main(String[] args)
{
      Scanner sc = new Scanner(System.in);
 int countPhotos = sc.nextInt();
 int timePhoto = sc.nextInt();
 int timeOrentir = sc.nextInt();
 int timeBig = sc.nextInt();
 char[] ch = new char[countPhotos];
 String h = sc.nextLine();
 for(int i = 0;i < h.length();i++)
 {
       ch[i] = h.charAt(i);
 }
 int time = 0;
 while(time == timeBig)
 {
       for(int i = 0,j = 1;i < countPhotos && j < countPhotos + 1;i++)
       {
             if(ch[i] == 'w' && ch[j] != 'w')
             {
                   time += timeOrentir;
                   time += timePhoto;
                   j++;
             }
       }
 }
 System.out.println(time);
}
}