#![allow(unused_imports)] #![allow(non_snake_case)] use std::collections::HashMap; use std::collections::HashSet; use std::collections::VecDeque; #[allow(unused_macros)] macro_rules! read { ([$t:ty] ; $n:expr) => ((0..$n).map(|_| read!([$t])).collect::>()); ($($t:ty),+ ; $n:expr) => ((0..$n).map(|_| read!($($t),+)).collect::>()); ([$t:ty]) => (rl().split_whitespace().map(|w| w.parse().unwrap()).collect::>()); ($t:ty) => (rl().parse::<$t>().unwrap()); ($($t:ty),*) => {{ let buf = rl(); let mut w = buf.split_whitespace(); ($(w.next().unwrap().parse::<$t>().unwrap()),*) }}; } #[allow(dead_code)] fn rl() -> String { let mut buf = String::new(); std::io::stdin().read_line(&mut buf).unwrap(); buf.trim_end().to_owned() } fn main() { let (mut x0, mut y0) = read!(f64, f64); let (mut x1, mut y1) = read!(f64, f64); if y0 > y1 { std::mem::swap(&mut x0, &mut x1); std::mem::swap(&mut y0, &mut y1); } println!("{}", y0 + ((y1 - y0) / (x0 + x1)) * x0); }