example = """
3   4
4   3
2   5
1   3
3   9
3   3
"""


parsed = [[],[]]

for x in open('input.txt', 'r').readlines():
# for x in example.splitlines():
    if x:
        a = [y for y in x.split(" ") if y]
        
        parsed[0].append(a[0])
        parsed[1].append(a[1])
        
parsed[0] = sorted(parsed[0])
parsed[1] = sorted(parsed[1])

parsed[0] = [int(x) for x in parsed[0]]
parsed[1] = [int(x) for x in parsed[1]]

asd = []

for x in parsed[0]:
    cnt = parsed[1].count(x)
    asd.append(x*cnt)

num = sum(asd)
print(num)