#[allow(unused_imports)]
use std::char::from_digit;
#[allow(unused_imports)]
use std::cmp::{max, min};
#[allow(unused_imports)]
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
#[allow(unused_imports)]
use std::fs::File;
#[allow(unused_imports)]
use std::io::prelude::*;
#[allow(unused_imports)]
use std::io::{stdin, stdout, BufReader, BufWriter, Stdin, Stdout, Write};
#[allow(unused_imports)]
use std::mem::swap;
#[allow(unused_imports)]
use std::str::FromStr;
 
type BoxResult<T> = Result<T, Box<std::error::Error>>;

const MAX: i64 = 1000;
const LIM: i64 = MAX + 1;
const RANGE: i64 = 2 * LIM + 1;
 
fn main() {
    let mut scanner = Scanner::new(stdin());
    let line = scanner.read_vector::<i64>().unwrap();
    let (sx, sy, tx, ty) = (line[0], line[1], line[2], line[3]);
    let mut used = vec![vec![false; RANGE as usize]; RANGE as usize];
    let mut path = vec![];
    for i in 0..4 {
        let mut p = if i % 2 == 0 {
            bfs(sx, sy, tx, ty, &mut used)
        } else {
            bfs(tx, ty, sx, sy, &mut used)
        };
        path.append(&mut p);
    }
    println!("{}", path.into_iter().collect::<String>());
}

fn bfs(sx: i64, sy: i64, tx: i64, ty: i64, used: &mut Vec<Vec<bool>>) -> Vec<char> {
    let mut visited = vec![vec![false; RANGE as usize]; RANGE as usize];
    let mut archive = vec![];
    let mut queue = VecDeque::new();
    let directions = vec![(-1, 0), (1, 0), (0, -1), (0, 1)];
    queue.push_front((sx, sy, 0, 0));
    visited[encode(sx)][encode(sy)] = true;
    while queue.len() > 0 {
        let (x, y, ox, oy) = queue.pop_back().unwrap();
        archive.push((x, y, ox, oy));
        if x == tx && y == ty {
            break;
        }
        for &(dx, dy) in directions.iter() {
            let new_x = x + dx;
            let new_y = y + dy;
            if !is_valid(new_x) || !is_valid(new_y) {
                continue;
            }
            let index_x = encode(new_x);
            let index_y = encode(new_y);
            if used[index_x][index_y] || visited[index_x][index_y] {
                continue;
            }
            queue.push_front((new_x, new_y, x, y));
            visited[index_x][index_y] = true;
        }
    }
    let mut path = vec![];
    let mut crt = archive.pop().unwrap();
    loop {
        let prv = archive.pop().unwrap();
        if crt.2 == prv.0 && crt.3 == prv.1 {
            if crt.0 > prv.0 {
                path.push('R');
            } else if crt.0 < prv.0 {
                path.push('L');
            } else if crt.1 > prv.1 {
                path.push('U');
            } else {
                path.push('D');
            }
            crt = prv;
            if crt.0 == sx && crt.1 == sy {
                break;
            }
            used[encode(crt.0)][encode(crt.1)] = true;
        }
    }
    path
}

fn encode(v: i64) -> usize {
    (v + MAX + 1) as usize
}

fn is_valid(v: i64) -> bool {
    v >= -MAX - 1 && v <= MAX + 1
}

#[allow(dead_code)]
struct Scanner<R> {
    reader: BufReader<R>,
    buffer: String,
}
impl<R> Scanner<R>
where
    R: Read,
{
    #[allow(dead_code)]
    fn new(inner: R) -> Scanner<R> {
        let reader = BufReader::new(inner);
        let buffer = String::new();
        Scanner {
            reader: reader,
            buffer: buffer,
        }
    }
    #[allow(dead_code)]
    fn with_capacity(capacity: usize, inner: R) -> Scanner<R> {
        let reader = BufReader::with_capacity(capacity, inner);
        let buffer = String::new();
        Scanner {
            reader: reader,
            buffer: buffer,
        }
    }
    #[allow(dead_code)]
    fn read_line(&mut self) -> BoxResult<String> {
        self.reader.read_line(&mut self.buffer)?;
        let cloned = self.buffer.trim().to_string();
        self.buffer.clear();
        Ok(cloned)
    }
    #[allow(dead_code)]
    fn read<T>(&mut self) -> BoxResult<T>
    where
        T: FromStr,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static,
    {
        self.reader.read_line(&mut self.buffer)?;
        let parsed = self.buffer.trim().parse()?;
        self.buffer.clear();
        Ok(parsed)
    }
    #[allow(dead_code)]
    fn read_two<T, U>(&mut self) -> BoxResult<(T, U)>
    where
        T: FromStr,
        T: Copy,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static,
        U: FromStr,
        U: Copy,
        U::Err: std::fmt::Debug,
        U::Err: std::error::Error,
        U::Err: 'static,
    {
        self.reader.read_line(&mut self.buffer)?;
        let (a, b) = {
            let params = self.buffer.trim().split_whitespace().collect::<Vec<_>>();
            let a = params[0].parse()?;
            let b = params[1].parse()?;
            (a, b)
        };
        self.buffer.clear();
        Ok((a, b))
    }
    #[allow(dead_code)]
    fn read_three<T>(&mut self) -> BoxResult<(T, T, T)>
    where
        T: FromStr,
        T: Copy,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static,
    {
        let nums = self.read_vector()?;
        Ok((nums[0], nums[1], nums[2]))
    }
    #[allow(dead_code)]
    fn read_vector<T>(&mut self) -> BoxResult<Vec<T>>
    where
        T: FromStr,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static,
    {
        self.reader.read_line(&mut self.buffer)?;
        let parsed_vec = self
            .buffer
            .trim()
            .split_whitespace()
            .map(|s| s.parse())
            .collect::<Result<Vec<_>, _>>()?;
        self.buffer.clear();
        Ok(parsed_vec)
    }
    #[allow(dead_code)]
    fn read_matrix<T>(&mut self, lines: usize) -> BoxResult<Vec<Vec<T>>>
    where
        T: FromStr,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static,
    {
        let mut parsed_matrix = vec![];
        for _ in 0..lines {
            self.reader.read_line(&mut self.buffer)?;
            parsed_matrix.push(
                self.buffer
                    .trim()
                    .split_whitespace()
                    .map(|s| s.parse())
                    .collect::<Result<Vec<_>, _>>()?,
            );
            self.buffer.clear();
        }
        Ok(parsed_matrix)
    }
    #[allow(dead_code)]
    fn read_chars(&mut self) -> BoxResult<Vec<char>> {
        self.reader.read_line(&mut self.buffer)?;
        let chars = self.buffer.trim().chars().collect::<Vec<_>>();
        self.buffer.clear();
        Ok(chars)
    }
}

Measured memory_bytes: 143464