# https://school.programmers.co.kr/learn/courses/30/lessons/120896
# programmers, level0: 한번만 등장한 문자, python3
def solution(s: str) -> str:
answer = ''
dict = {}
for x in s:
if x not in dict:
dict[x] = 1
else:
dict[x] += 1
for x in dict:
if dict[x] == 1:
answer += x
return ''.join(map(str, sorted(answer)))
if __name__ == '__main__':
print(solution("abcabcadc"))
print(solution("abdc"))
print(solution("hello"))