Frequency of letters in a string in c#

public class Frequency

{

    static void Main()

    {

        char ch;

        Console.WriteLine("Enter a string:");

        string str = Console.ReadLine();

        for (ch = 'A'; ch <= 'Z'; ch++)

        {

            int count = 0;

            for (int i = 0; i < str.Length; i++)

            {

                if (ch == str[i] || str[i] == (ch + 32))

                {

                    count++;

                }

            }

            if (count > 0)

            {

                Console.WriteLine("Char {0} having Freq of {1}", (char)(ch + 32), count);

            }

        }

        Console.ReadLine();

    }

}

Output: