using System;

using System.Text.RegularExpressions;                   

public class Program

{

    public static void Main()

    {

        string textWithCityNames = "Varna, Plovdiv, Burgas, Ruse, Radomir, Biala, Sofia, Vidin, Sredec, VTarnovo";

        Regex regex = new Regex(@"\b[S]\w+");

        MatchCollection cityMatch = regex.Matches(textWithCityNames);

        foreach(Match match in cityMatch)

        {

            Console.WriteLine("City name with S: {0}, Index: {1}" , match.Value, match.Index);

        }

        Regex regex2 = new Regex(@"\b[V]\w+");

        MatchCollection cityMatch2 = regex2.Matches(textWithCityNames);

        foreach(Match match2 in cityMatch2)

        {

            Console.WriteLine("City name with V: {0}, Index: {1}", match2.Value, match2.Index);

        }

        Regex regex3 = new Regex(@"\b[B]\w+");

        MatchCollection cityMatch3 = regex3.Matches(textWithCityNames);

        foreach(Match match3 in cityMatch3)

        {

            Console.WriteLine("City name with B: {0}, Index: {1}", match3.Value, match3.Index);

        }

    }

}