Problem:
Score : 100 points

Problem Statement

It is known that the area of a regular dodecagon inscribed in a circle of radius a is 3a^2.

Given an integer r, find the area of a regular dodecagon inscribed in a circle of radius r.

Constraints

1 \leq r \leq 100

r is an integer.

Input

Input is given from Standard Input in the following format:

r

Output

Print an integer representing the area of the regular dodecagon.

Sample Input 1

4

Sample Output 1

48

The area of the regular dodecagon is 3 \times 4^2 = 48.

Sample Input 2

15

Sample Output 2

675

Sample Input 3

80

Sample Output 3

19200

Solution in Rust (1.15.1) (judge verdict: Runtime Error)

use std::io::*;
use std::str::FromStr;

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

fn main() {
    let n: i32 = read();
    let mut vec: Vec<i32> = vec![];
    for _ in 0..n {
        vec.push(read());
    }
    // for (i, v) in vec.iter().enumerate().map(|(x, y)| (x + 1, y)).rev() {
    let mut rev_ans = vec![0; vec.len()];
    let mut m = 0;
    let mut ans = vec![];
    for (i_1, _) in vec.iter().enumerate().rev() {
        let i = i_1 + 1;
        let mut sum = 0;
        for j in 1..(vec.len() / i) {
            // eprintln!(
            //     "i:{}, v:{}, rev_ans:{:?}, vec.len:{}, j:{}",
            //     i,
            //     v,
            //     rev_ans,
            //     vec.len(),
            //     j
            // );
            sum += rev_ans[(i * j) - 1];
        }
        if sum % 2 == vec[i_1] {
            rev_ans[i_1] = 0;
        } else {
            rev_ans[i_1] = 1;
            ans.push(i);
            m += 1;
        }
    }
    println!("{}", m);
    println!(
        "{}",
        ans.iter()
            .map(|i| i.to_string())
            .collect::<Vec<String>>()
            .join(" ")
    );
}