The program Telephone Digits outputs only telephone digits that correspond to uppercase letters.

Rewrite the program so that it processes both uppercase and lowercase letters and outputs the corresponding telephone digit.

If the input is something other than an uppercase or lowercase letter, the program must output an appropriate error message $($The error message should contain the phrase Invalid input$).$

Task #$01$: Correct output for lowercase test cases

Task #$02$: Correct output for lowercase and uppercase test cases