sum = 0

list1 = []
list2 = []

with open("input") as f:
    for line in f.readlines():
        nums = line.split()
        list1.append(int(nums[0]))
        list2.append(int(nums[1]))

memoize_count = {}

for num in list1:
    if num not in memoize_count.keys():
        memoize_count[num] = list2.count(num)

    sum += memoize_count[num] * num

print(sum)