import java.util.Stack;
import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while(in.hasNextInt()){
            int n = in.nextInt();
            int a[][] = new int[n][2];
            for(int i=0;i<n;i++){
                a[i][0] = in.nextInt();
                a[i][1] = in.nextInt();
            }
            String s = in.next();
            Stack<Integer> stack = new Stack();                 // 存放矩阵行数和列数
            int sum = 0;
            for(int i=s.length()-1,j=n-1;i>=0;i--){
                if(s.charAt(i)>='A' && s.charAt(i)<='Z'){       // 属于字母则把相应的矩阵列数和行数入栈
                    stack.push(a[j][1]);
                    stack.push(a[j][0]);
                    j--;
                }else if(s.charAt(i) == '('){                   // 括号:推出计算
                    int x0 = stack.pop(), y0 = stack.pop();     // 矩阵尺寸x0*y0
                    int x1 = stack.pop(), y1 = stack.pop();     // 矩阵尺寸x1*y1
                    sum += x0*y0*y1;      // 两个矩阵的乘法次数为x0*y0*y1或x0*x1*y1(其中y0==x1)
                    stack.push(y1);       // 把相乘后得到的矩阵列数入栈
                    stack.push(x0);       // 把相乘后得到的矩阵行数入栈
                }
            }
            System.out.println(sum);
        }
    }
}