Problem:
Score : 200 points

Problem Statement

Takahashi loves gold coins. He gains 1000 happiness points for each 500-yen coin he has and gains 5 happiness points for each 5-yen coin he has. (Yen is the currency of Japan.)

Takahashi has X yen. If he exchanges his money so that he will gain the most happiness points, how many happiness points will he earn?

(We assume that there are six kinds of coins available: 500-yen, 100-yen, 50-yen, 10-yen, 5-yen, and 1-yen coins.)

Constraints

0 \leq X \leq 10^9

X is an integer.

Input

Input is given from Standard Input in the following format:

X

Output

Print the maximum number of happiness points that can be earned.

Sample Input 1

1024

Sample Output 1

2020

By exchanging his money so that he gets two 500-yen coins and four 5-yen coins, he gains 2020 happiness points, which is the maximum number of happiness points that can be earned.

Sample Input 2

0

Sample Output 2

0

He is penniless - or yenless.

Sample Input 3

1000000000

Sample Output 3

2000000000

He is a billionaire - in yen.

Solution in Rust (1.15.1) (judge verdict: Wrong Answer)

use std::io::Read;

fn main() {
    let i = input();
    println!("{}", solve(i));
}

fn input() -> usize {
    let mut buf = String::from("");
    std::io::stdin().read_line(&mut buf).unwrap();
    println!("buf = {}", buf);
    buf.pop();
    let i: usize = buf.parse().unwrap();
    i
}

fn solve(input: usize) -> usize {
    if input == 0 {
        return 0;
    }

    let number_500 = input / 500;
    let remain = input - (number_500 * 500);
    let number_5 = remain / 5;

    number_500 * 1000 + number_5 * 5
}