In c++ please

2. Demonstrate by writing a program to calculate the frequency of every letter in an input string s. a. Your program should be able to input a string. b. Your message should be constructed from at least 50 letters. c. Calculate the frequency of each element in the string and store the results into a linked list. d. Your program should be able to print each letter and its respective frequency. e. Identify the letter with the highest frequency in your message. f. Sort the linked list in ascending order using an algorithm of your choice. Write a short justification of your choice. Example of Output: Input a string: ......... letters frequency 1 r b 4 6 f 12 S 20 e 24 a 30 Letter s has the highest frequency of 20