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)