题解 | #矩阵乘法计算量估算#

import sys
#矩阵相乘的乘法数,和结果矩阵
def com_count(listA, listB):
    count = listA[0] * listA[1] * listB[1]
    listC = [listA[0], listB[1]]
    return count, listC

while True:
    try:
        n = int(input())
        #先将矩阵保存
        mn_list = []
        for i in range(n):
            m, n = map(int,input().split())
            mn_list.append([m, n])
        gz = input()
        count = 0
        stack = []  #使用栈处理
        for c in gz:
            if c == '(':
                continue
            elif c == ')':#对于')'，连续出栈两个矩阵，计算出乘法次数和结果矩阵
                if len(stack) <= 1:
                    break
                addc, m = com_count(stack.pop(-2), stack.pop())
#                 print(addc, m)
                stack.append(m)
                count += addc
            else:
                stack.append(mn_list.pop(0)) #碰到字母就压栈
        print(count)

    except:
#         print(sys.exc_info())
        break


























# import sys
# #矩阵相乘的乘法数,和结果矩阵
# def com_count(listA, listB):
#     count = listA[0] * listA[1] * listB[1]
#     listC = [listA[0], listB[1]]
#     return count, listC

# while True:
#     try:
#         n = int(input())
#         #按大写字母保存对应的矩阵
#         mn_dic = {}
#         for i in range(n):
#             m, n = map(int,input().split())
#             mn_dic[chr(i + 65)] = [m, n]
#         gz_list = list(input())
# #         print(mn_dic)
#         count = 0
#         i = 0
#         while i < len(gz_list) - 1 and len(gz_list) >= 3:
#             #连续字母,直接相乘,把结果矩阵对应在左边字母
#             if gz_list[i].isalpha() and gz_list[i + 1].isalpha():
#                 addc, mn_dic[gz_list[i]] = com_count(mn_dic[gz_list[i]], mn_dic[gz_list[i + 1]])
#                 count += addc
#                 #删掉右边字母
#                 del gz_list[i + 1]
#                 #如果左右都是括号,也删掉括号
#                 if gz_list[i - 1] == '(' and gz_list[i + 1] == ')':
#                     del gz_list[i + 1]
#                     del gz_list[i - 1]
#                     i -= 2
#             else:
#                 i += 1
#         print(count)

#     except:
# #         print(sys.exc_info())
#         break