Should return the least frequent letter in a word str

Write a function 'leastFrequentLetter(string)' that will take a string as an argument and return the character that appears the least often. In case of a tie, return any character with the lowest count. The string witl have at least one character. Exanples: leastfrequentLetter("mississippi") /1nm leastfrequentLetter ("ananab") /1 "b" leastfrequentLetter("Cheese") /1 "C", "h", or "s