using System;

using System.Text.RegularExpressions;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine(HighestOccuringWord("This is really really great great great "));

    }

​

    public static string HighestOccuringWord(string str)

    {

        string[] strArray = Regex.Split(str, @"\s+");

        Dictionary<String, int> dict = new Dictionary<String, int>();

        int count = 0;

        string maxWord = strArray[0];

        for (int i = 0; i < strArray.Length; i++)

        {

            if (!dict.ContainsKey(strArray[i]))

            {

                dict.Add(strArray[i], 0);

                //Console.WriteLine(strArray[i]);

                if (dict[strArray[i]] > count)

                {

                    count = dict[strArray[i]];

                    maxWord = strArray[i];

                }

            }

            else

            {

                dict[strArray[i]]++;

                if (dict[strArray[i]] > count)

                {

                    count = dict[strArray[i]];

                    maxWord = strArray[i];

                }

            }

        }

        return maxWord;

    }

}