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: Accepted)

mod stdin_reader {
  use std::io::stdin;
  use std::io::Read;

  pub struct StdinReader {
    pub buf: Vec<String>,
    pub cursor: usize,
  }

  pub fn new() -> StdinReader {
    StdinReader::new()
  }

  impl StdinReader {
    pub fn new() -> Self {
      let mut s = String::new();
      let stdin = stdin();
      stdin.lock().read_to_string(&mut s).unwrap();
      let buf = s.split_whitespace().map(|s| s.to_string()).collect();
      return StdinReader { buf: buf, cursor: 0 }
    }

    pub fn read_all(&self) -> Vec<String> {
      return self.buf.clone()
    }

    pub fn next(&mut self) -> Option<String> {
      let val = self.buf.get(self.cursor).cloned();
      self.cursor += 1;
      return val
    }

    pub fn as_i64(&mut self) -> Option<i64> {
      self.next().and_then(|s| s.parse::<i64>().ok())
    }

    pub fn as_f64(&mut self) -> Option<f64> {
      self.next().and_then(|s| s.parse::<f64>().ok())
    }

    pub fn as_usize(&mut self) -> Option<usize> {
      self.next().and_then(|s| s.parse::<usize>().ok())
    }
  }
}

mod utils {
  pub fn is_int(n: f64) -> bool {
    let trunc = (n.trunc() as i64) as f64;
    return (n - trunc) < 0.0001
  }
}

fn main() {
  // stdout
  use std::io::{stdout, Write, BufWriter};
  let stdout = stdout();
  let mut writer = BufWriter::new(stdout.lock());

  // stdin
  let mut reader = stdin_reader::new();

  let r = reader.as_i64().unwrap();
  println!("{}", 3 * r * r);
}