fn main() {
    let mut xx = String::new();
    std::io::stdin().read_line(&mut xx).ok();
    let xx: Vec<f64> = xx.split_whitespace().flat_map(str::parse).collect();

    if xx[3] / xx[2] >= xx[1] / xx[0] {
        println!("{}", (1. + xx[1] / xx[0]) * xx[2]);
    } else {
        println!("{}", (1. + xx[0] / xx[1]) * xx[3]);
    }
}