use std::f64::consts::PI;

fn main() {
    let mut c = String::new();
    std::io::stdin().read_line(&mut c).ok();
    let c: usize = c.trim().parse().unwrap();
    let mut xy = String::new();
    std::io::stdin().read_line(&mut xy).ok();
    let xy: Vec<usize> = xy.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let x = xy[0];
    let y = xy[1];

    let r: f64 = (y - x) as f64 / 2.0;
    let s: f64 = PI * r * r;
    let large_r: f64 = (y - x) as f64 / 2.0 + x as f64;
    println!("{}", c as f64 * 2.0 * PI * large_r * s);
}