using System;

public class Program

{

    public static void Main()

    {

        var data = new [] {"A", "B", "C", "D", "E", 

                           "F", "G", "H", "I", "J", 

                           "K", "L", "M", "N", "O", 

                           "P", "Q", "R", "S", "T"

                          };

        const int elementsPerRow = 5;

        var aIndex = GetIndex(0, 0, elementsPerRow);

        var eIndex = GetIndex(0, 4, elementsPerRow);

        var pIndex = GetIndex(3, 0, elementsPerRow);

        var tIndex = GetIndex(3, 4, elementsPerRow);

        Console.WriteLine(data[aIndex]);

        Console.WriteLine(data[eIndex]);

        Console.WriteLine(data[pIndex]);

        Console.WriteLine(data[tIndex]);

    }

    public static int GetIndex(int rowIndex, int columnIndex, int elementsPerRow) {

        var index = rowIndex * elementsPerRow + columnIndex;

        return index;

    }

}