use std::fs::File;
use std::io::{self, BufRead};
use std::path::Path;
use std::collections::HashMap;
use std::env;

fn read_lines<P>(filename: P) -> io::Result<io::Lines<io::BufReader<File>>>
where P: AsRef<Path>, {
    let file = File::open(filename)?;
    Ok(io::BufReader::new(file).lines())
}

fn main() {
    let mut occurrences: HashMap<i32, i32> = HashMap::new();
    let mut left_list: Vec<i32> = vec![];
    let mut right_list: Vec<i32> = vec![];

    let args: Vec<_> = env::args().collect();

    if let Ok(lines) = read_lines(args[1].clone()) {
        for line in lines.flatten() {
            let parts = line.split("   ").collect::<Vec<_>>();
            let lnum = parts[0].parse::<i32>().unwrap();
            let rnum = parts[1].parse::<i32>().unwrap();
            left_list.push(lnum);
            right_list.push(rnum);
        }
        for left_n in left_list {
            let entry = occurrences.entry(left_n).or_insert(0);
            for right_n in &right_list {
                if left_n == *right_n {
                    *entry += 1;
                }
            }
        }

        let mut sum = 0;
        for (num, count) in &occurrences {
            sum += num * count;
        }
        println!("{}", sum)
    }
}