fn main() { let x: f32 = { let mut line: String = String::new(); std::io::stdin().read_line(&mut line).unwrap(); line.trim().parse().unwrap() }; let mut ANS:f32=0.0000000005; for i in 1..1200000000{ ANS+=1.0/((i as f32 +x)*(i as f32 +x)); } println!("{}",ANS); }