use std::io::{self, BufRead};

fn main() -> io::Result<()> {
    let mut total: i64 = 0;
    io::stdin()
        .lock()
        .lines()
        .filter_map(|l| l.ok())
        .filter_map(|l| l.parse::<i64>().ok())
        .for_each(|line| {
            let mut cost = fuel_cost(line);
            while cost > 0 {
                total += cost;
                cost = fuel_cost(cost);
            }
        });

    println!("total fuel needed: {}", total);
    Ok(())
}

fn fuel_cost(mass: i64) -> i64 {
    mass / 3 - 2
}