use std::cmp::*;
use std::collections::BTreeSet;
use std::io::*;
use std::str::FromStr;
//portable utility
#[allow(dead_code)]
fn switch<T>(flag: bool, true_value: T, false_value: T) -> T {
    if flag {
        true_value
    } else {
        false_value
    }
}
#[allow(dead_code)]
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")
}
#[allow(dead_code)]
fn read_string() -> Vec<char> {
    read::<String>().chars().collect()
}
#[allow(dead_code)]
fn read_vector<T: FromStr>(number: usize) -> Vec<T> {
    (0..number).map(|_| read()).collect()
}
fn main() {
    let r: f32 = read();
    println!("{}", r * r * std::f32::consts::PI);
}
