fn main() { let x: f64 = { let mut line: String = String::new(); std::io::stdin().read_line(&mut line).unwrap(); line.trim().parse().unwrap() }; let mut ANS:f64=0.0; for i in 1..1000000000{ ANS+=1.0/((i as f64 +x)*(i as f64 +x)); } ANS+=1.0/(x+1000000000.0); println!("{}",ANS); }