#!/usr/bin/env python
# 2024 - Advent Of Code 1 - part 2

# file = 'input_example.txt'
file = 'input.txt'

firsts = []
seconds = {}
accum = 0
with open(file, encoding="utf-8") as f:
    for line in f.readlines():
        a, b, c, d = line.strip().split(' ')
        firsts.append(int(a))
        if int(d) in seconds:
            seconds[int(d)] += 1
        else:
            seconds[int(d)] = 1

for num in firsts:
    if num in seconds:
        accum += num * seconds[num]

print(f"sum: {accum}")