For a given input string, capitalize every letter at the beginning of a word, and transform the rest of the letters to lower-case.
Non-letter characters should remain the same.
You can assume there is only one space between every two words.
input: 'this is BETTER than C++' output: 'This Is Better Than C++'
input: 'hEy, tHis iS vErY wroNg!' output: 'Hey, This Is Very Wrong!'