Write a function that will return the count of distinct case-insensitive alphabetic characters that occur more than once in the given string. The given string can be assumed to contain only digits and uppercase and lowercase alphabets.
Example
"abcde" -> 0 # no characters repeats more than once "aabbcde" -> 2 # 'a' and 'b' "aabbcdeB" -> 2 # 'a' and 'b' "indivisibility" -> 1 # 'i' "Indivisibilities" -> 2 # 'i' and 's'
Finish the solution so that it returns the sum of all the multiples of 3 or 5 below the number passed in.
Courtesy of ProjectEuler.net