#![allow(unused_imports)]
#![allow(non_snake_case)]
use std::collections::HashMap;
use std::collections::HashSet;

#[allow(unused_macros)]
macro_rules! read {
    ([$t:ty] ; $n:expr) =>
        ((0..$n).map(|_| read!([$t])).collect::<Vec<_>>());
    ($($t:ty),+ ; $n:expr) =>
        ((0..$n).map(|_| read!($($t),+)).collect::<Vec<_>>());
    ([$t:ty]) =>
        (rl().split_whitespace().map(|w| w.parse().unwrap()).collect::<Vec<$t>>());
    ($t:ty) =>
        (rl().parse::<$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 dist = read!(i32, i32);
    let obst = read!(i32, i32);

    let min = (dist.0).abs().max((dist.1).abs());

    if ((dist.0).abs() == dist.1) && (obst.0 == obst.1) {
        if (dist.0 ^ obst.0 >= 0) && (dist.1 ^ obst.1 > 0) {
            if dist.0.abs() > obst.0.abs() {
                println!("{}", min + 1);
                return;
            }
        }
    }

    println!("{}", min);
}