using System;

using System.Linq;

​

public class Program

{

    public void Main()

    {

        Func("hello world blabla bla");

    }

    public static void Func(string str)

    {

        var revStr = str.ToArray();

        Reverce(revStr, 0, str.Length-1);

        var wordStart = 0;

        for (var i = 0; i < revStr.Length; i++)

        {

            if (revStr[i] == ' ')

            {

                Reverce(revStr, wordStart, i - 1);

                wordStart = i+1;

            }

            if(i==revStr.Length-1)

                Reverce(revStr, wordStart, i);

        }

        Console.WriteLine(new string(revStr));

    }

    private static void Reverce(char[] ch, int s, int e)

    {

        for (var i = s; i <= (s+e)/2; i++)

        {

            var tmp = ch[i];

            ch[i] = ch[s + e - i];

            ch[s + e - i] = tmp;

        }

    }

}