#!/usr/bin/python

with open('01a.txt') as f:
    text = f.read().strip()

lines = text.split('\n')

a = [None] * len(lines)
b = [None] * len(lines)

for i in range(len(lines)):
    spl = lines[i].split(' ', maxsplit=1)
    a[i] = int(spl[0].strip())
    b[i] = int(spl[1].strip())

a.sort()
b.sort()

total = 0

# for x, y in zip(a, b):
#     total += abs(x - y)

# print(total)

i_a = 0
i_b = 0

while i_a < len(lines) and i_b < len(lines):
    x_a = a[i_a]
    x_b = b[i_b]
    if x_a == x_b:
        total += x_b
        i_b += 1
    elif x_a < x_b:
        i_a += 1
    else:
        i_b += 1

print(total)