def firstNonRepeatingLetter(word):
    for char in word:
        if word.lower().count(char.lower()) == 1 :
            return char
    return ""
# manuel Testing
print(firstNonRepeatingLetter("sTreSS"))
print(firstNonRepeatingLetter("sdasddd"))
print(firstNonRepeatingLetter("wWw"))