using System;

public class Program

{

    public static void Main()

    {

        string vkDateTime = "02.04.1988";

        int firstDot = vkDateTime.IndexOf('.');

        int secondDot = vkDateTime.IndexOf('.', firstDot + 1);

​

        //int day = int.Parse(vkDateTime.Substring(0, firstDot));

        int month = 0;

        //Console.WriteLine(day);

        Console.WriteLine(vkDateTime.Substring(firstDot + 1, secondDot));

    }

}