using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var sentence ="my name is john. i am 23 years old.";

        string[] words = sentence.Split(' ');

        Array.Reverse(words);

        var result = words.Select(x => x.EndsWith('.') ? $".{x.Trim('.')}" : x);

        Console.WriteLine(string.Join(" ", result));

    }

}