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

fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let n: usize = s.trim().parse().unwrap();

    let mut ans: f64 = 0.;
    for _ in 0..n {
        let mut s = String::new();
        std::io::stdin().read_line(&mut s).ok();
        let mut itr = s.trim().split_whitespace();
        ans += itr.skip(1).next().unwrap().parse::<f64>().unwrap();
    }
    println!("{}", ans * PI);
}