Problem:
Score : 300 points

Problem Statement

Dolphin resides in two-dimensional Cartesian plane, with the positive x-axis pointing right and the positive y-axis pointing up.

Currently, he is located at the point (sx,sy). In each second, he can move up, down, left or right by a distance of 1.

Here, both the x- and y-coordinates before and after each movement must be integers.

He will first visit the point (tx,ty) where sx < tx and sy < ty, then go back to the point (sx,sy), then visit the point (tx,ty) again, and lastly go back to the point (sx,sy).

Here, during the whole travel, he is not allowed to pass through the same point more than once, except the points (sx,sy) and (tx,ty).

Under this condition, find a shortest path for him.

Constraints

-1000 ≤ sx < tx ≤ 1000

-1000 ≤ sy < ty ≤ 1000

sx,sy,tx and ty are integers.

Input

The input is given from Standard Input in the following format:

sx sy tx ty

Output

Print a string S that represents a shortest path for Dolphin.

The i-th character in S should correspond to his i-th movement.

The directions of the movements should be indicated by the following characters:

U: Up

D: Down

L: Left

R: Right

If there exist multiple shortest paths under the condition, print any of them.

Sample Input 1

0 0 1 2

Sample Output 1

UURDDLLUUURRDRDDDLLU

One possible shortest path is:

Going from (sx,sy) to (tx,ty) for the first time: (0,0) → (0,1) → (0,2) → (1,2)

Going from (tx,ty) to (sx,sy) for the first time: (1,2) → (1,1) → (1,0) → (0,0)

Going from (sx,sy) to (tx,ty) for the second time: (0,0) → (-1,0) → (-1,1) → (-1,2) → (-1,3) → (0,3) → (1,3) → (1,2)

Going from (tx,ty) to (sx,sy) for the second time: (1,2) → (2,2) → (2,1) → (2,0) → (2,-1) → (1,-1) → (0,-1) → (0,0)

Sample Input 2

-2 -2 1 1

Sample Output 2

UURRURRDDDLLDLLULUUURRURRDDDLLDL

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Linq;
using System.Collections.Generic;
using Debug = System.Diagnostics.Debug;
using StringBuilder = System.Text.StringBuilder;
using System.Numerics;
//using Point = System.Numerics.Complex;
using Number = System.Int64;
namespace Program
{
    public class Solver
    {
        public void Solve()
        {
            var a = sc.Integer(4);
            var dx = a[2] - a[0];
            var dy = a[3] - a[1];
            var sb = new StringBuilder();
            for (int i = 0; i < dy; i++)
                sb.Append('U');
            for (int i = 0; i < dx; i++)
                sb.Append('R');
            for (int i = 0; i < dy; i++)
                sb.Append('D');
            for (int i = 0; i < dx; i++)
                sb.Append('L');
            sb.Append('L');
            for (int i = 0; i < dy + 1; i++)
                sb.Append('U');
            for (int i = 0; i < dx + 1; i++)
                sb.Append('R');
            sb.Append('D');
            sb.Append('R');
            for (int i = 0; i < dy + 1; i++)
                sb.Append('D');
            for (int i = 0; i < dx + 1; i++)
                sb.Append('L');
            sb.Append('U');
            IO.Printer.Out.WriteLine(sb.ToString());
        }
        ModInteger f(long k)
        {
            var mat = new Matrix(2, 2);
            mat[0, 0] = mat[0, 1] = 1;
            mat[1, 0] = 1;
            var ret = Matrix.Pow(mat, k);
            return ret[0, 0] + ret[0, 1];
        }

        public IO.StreamScanner sc = new IO.StreamScanner(Console.OpenStandardInput());
        static T[] Enumerate<T>(int n, Func<int, T> f) { var a = new T[n]; for (int i = 0; i < n; ++i) a[i] = f(i); return a; }
        static public void Swap<T>(ref T a, ref T b) { var tmp = a; a = b; b = tmp; }
    }
}

#region main
static class Ex
{
    //static public string AsString(this IEnumerable<char> ie) { return new string(System.Linq.Enumerable.ToArray(ie)); }
    //static public string AsJoinedString<T>(this IEnumerable<T> ie, string st = " ") { return string.Join(st, ie); }
    static public void Main()
    {
        var solver = new Program.Solver();
        solver.Solve();
        Program.IO.Printer.Out.Flush();
    }
}
#endregion
#region Ex
namespace Program.IO
{
    using System.IO;
    using System.Text;
    using System.Globalization;
    public class Printer: StreamWriter
    {
        static Printer() { Out = new Printer(Console.OpenStandardOutput()) { AutoFlush = false }; }
        public static Printer Out { get; set; }
        public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
        public Printer(System.IO.Stream stream) : base(stream, new UTF8Encoding(false, true)) { }
        public Printer(System.IO.Stream stream, Encoding encoding) : base(stream, encoding) { }
        public void Write<T>(string format, T[] source) { base.Write(format, source.OfType<object>().ToArray()); }
        public void WriteLine<T>(string format, T[] source) { base.WriteLine(format, source.OfType<object>().ToArray()); }
    }
    public class StreamScanner
    {
        public StreamScanner(Stream stream) { str = stream; }
        public readonly Stream str;
        private readonly byte[] buf = new byte[1024];
        private int len, ptr;
        public bool isEof = false;
        public bool IsEndOfStream { get { return isEof; } }
        private byte read()
        {
            if (isEof) return 0;
            if (ptr >= len) { ptr = 0; if ((len = str.Read(buf, 0, 1024)) <= 0) { isEof = true; return 0; } }
            return buf[ptr++];
        }
        public char Char() { byte b = 0; do b = read(); while ((b < 33 || 126 < b) && !isEof); return (char)b; }

        public string Scan()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b >= 33 && b <= 126; b = (char)read())
                sb.Append(b);
            return sb.ToString();
        }
        public string ScanLine()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b != '\n'; b = (char)read())
                if (b == 0) break;
                else if (b != '\r') sb.Append(b);
            return sb.ToString();
        }
        public long Long()
        {
            if (isEof) return long.MinValue;
            long ret = 0; byte b = 0; var ng = false;
            do b = read();
            while (b != 0 && b != '-' && (b < '0' || '9' < b));
            if (b == 0) return long.MinValue;
            if (b == '-') { ng = true; b = read(); }
            for (; true; b = read())
            {
                if (b < '0' || '9' < b)
                    return ng ? -ret : ret;
                else ret = ret * 10 + b - '0';
            }
        }
        public int Integer() { return (isEof) ? int.MinValue : (int)Long(); }
        public double Double() { var s = Scan(); return s != "" ? double.Parse(s, CultureInfo.InvariantCulture) : double.NaN; }
        private T[] enumerate<T>(int n, Func<T> f)
        {
            var a = new T[n];
            for (int i = 0; i < n; ++i) a[i] = f();
            return a;
        }

        public char[] Char(int n) { return enumerate(n, Char); }
        public string[] Scan(int n) { return enumerate(n, Scan); }
        public double[] Double(int n) { return enumerate(n, Double); }
        public int[] Integer(int n) { return enumerate(n, Integer); }
        public long[] Long(int n) { return enumerate(n, Long); }
    }
}
#endregion

#region Matrix
public class Matrix
{
    int row, col;
    public Number[] mat;
    public Number this[int r, int c]
    {
        get { return mat[r * col + c]; }
        set { mat[r * col + c] = value; }
    }
    public Matrix(int r, int c)
    {
        row = r; col = c;
        mat = new Number[row * col];
    }
    public static Matrix operator +(Matrix l, Matrix r)
    {
        check(l, r);
        var ret = new Matrix(l.row, l.col);
        for (int i = 0; i < l.row; i++)
            for (int j = 0; j < l.col; j++)
                ret.mat[i * ret.col + j] = l.mat[i * l.col + j] + r.mat[i * r.col + j];
        return ret;

    }
    public static Matrix operator *(Matrix l, Matrix r)
    {
        checkMul(l, r);
        var ret = new Matrix(l.row, r.col);
        for (int i = 0; i < l.row; i++)
            for (int k = 0; k < l.col; k++)
                for (int j = 0; j < r.col; j++)
                    ret.mat[i * r.col + j] = (ret.mat[i * r.col + j] + l.mat[i * l.col + k] * r.mat[k * r.col + j]);
        return ret;
    }
    public static Matrix Pow(Matrix m, long n)
    {
        var ret = new Matrix(m.row, m.col);
        for (int i = 0; i < m.row; i++)
            ret.mat[i * m.col + i] = 1;
        for (; n > 0; m *= m, n >>= 1)
            if ((n & 1) == 1)
                ret = ret * m;
        return ret;

    }
    public static Matrix[] PowTable(Matrix m, int k)
    {
        var ret = new Matrix[k];
        ret[0] = m;
        for (int i = 1; i < k; i++)
            ret[i] = ret[i - 1] * ret[i - 1];
        return ret;
    }
    public static Matrix PowWithTable(Matrix m, long n, Matrix[] table)
    {
        var ret = new Matrix(m.row, m.col);
        for (int i = 0; i < m.row; i++)
            ret.mat[i * m.col + i] = 1;
        for (int i = 0; i < table.Length; i++)
        {
            if ((n & 1) == 1) ret = ret * table[i];
        }
        return ret;
    }
    public static Matrix Trans(Matrix m)
    {
        var ret = new Matrix(m.col, m.row);
        for (int i = 0; i < m.row; i++)
            for (int j = 0; j < m.col; j++)
                ret.mat[j * m.col + i] = m.mat[i * m.col + j];
        return ret;
    }
    [System.Diagnostics.Conditional("DEBUG")]
    static private void check(Matrix a, Matrix b)
    {
        if (a.row != b.row || a.col != b.col)
            throw new Exception("row and col have to be same.");

    }
    [System.Diagnostics.Conditional("DEBUG")]
    static private void checkMul(Matrix a, Matrix b)
    {
        if (a.col != b.row)
            throw new Exception("row and col have to be same.");
    }
    public Number[][] Items
    {
        get
        {
            var a = new Number[row][];
            for (int i = 0; i < row; i++)
            {
                a[i] = new Number[col];
                for (int j = 0; j < col; j++)
                    a[i][j] = mat[i * col + j];
            }
            return a;
        }
    }
    public override string ToString()
    {
        return string.Format("{0}*{1}", row, col);
    }
}
#endregion
#region ModNumber
public partial struct ModInteger
{
    public const long Mod = (long)1e9 + 7;
    public long num;
    public ModInteger(long n) : this() { num = n % Mod; if (num < 0) num += Mod; }
    public override string ToString() { return num.ToString(); }
    public static ModInteger operator +(ModInteger l, ModInteger r) { var n = l.num + r.num; if (n >= Mod) n -= Mod; return new ModInteger() { num = n }; }
    public static ModInteger operator -(ModInteger l, ModInteger r) { var n = l.num + Mod - r.num; if (n >= Mod) n -= Mod; return new ModInteger() { num = n }; }
    public static ModInteger operator *(ModInteger l, ModInteger r) { return new ModInteger(l.num * r.num); }
    public static ModInteger operator ^(ModInteger l, long r) { return ModInteger.Pow(l, r); }
    public static implicit operator ModInteger(long n) { return new ModInteger() { num = n }; }
    public static ModInteger Pow(ModInteger v, long k)
    {
        ModInteger ret = 1;
        var n = k;
        for (; n > 0; n >>= 1, v *= v)
        {
            if ((n & 1) == 1)
                ret = ret * v;
        }
        return ret;
    }
}
#endregion