using System;

public class Program

{

    public static void Main()

    {

        string s="Здравей,Ани,изпратих ти писмо";

        string s2=s.Replace("Ани","Мими");

        string s3=s2.Replace("писмо","цветя"); 

        string sub=s.Substring(6,2);

​

        Console.WriteLine(s);

        Console.WriteLine(s2);

        Console.WriteLine(s3);

    }

}