using System;

public class Program

{

    public static void Main()

    {

        string s = "Informatics";

            string s1 = s.Substring(2, 4);

            Console.WriteLine(s1);

​

            string a = "Poluchatel: Petur Petrov";

            string a1 = a.Replace("Pet", "Dimit");

            Console.WriteLine("a1");

    }

}