题解 | #矩阵乘法计算量估算#

# 2024年10月31日   周四  上午11:36

"""
3
50 10
10 20
20 5
(A(BC))
"""
n = int(input())  # 要计算乘法的矩阵个数n
ls = []
for i in range(n):
    ls.append(list(map(int, input().split())))
#print(ls)
f = input()
#print(f)
stack = []
p = 0
for i in f:
    if i.isalpha():
        stack.append(ls[ord(i) - 65])
    elif i == ")" and len(stack) >= 2:
        c = stack.pop()  # C
        b = stack.pop()  # B
        p += b[0] * b[1] * c[1]  # p = m*n*p，注意顺序
        stack.append([b[0], c[1]])

print(p)