n = input() len_n = len(n) min_word = 1 while True: for i in n: #print(i) if n.count(i)==min_word: # 最小值为一，把是一的替换 n =n.replace(i, '')

if len_n == len(n):      # 如果长度相等就是没有替换
    min_word = min_word+1       # 最小值增大
    continue
    
else:
    print(n)
    break