# 处理输入
str_1 = input()
# 找出最小
min_1 = str_1.count(str_1[0])
lsit_1 = []
for i in str_1:
    lsit_1.append(i)
    if str_1.count(i) < min_1:
        min_1 = str_1.count(i)
# 替换
for i in lsit_1:
    if str_1.count(i) == min_1:
        str_1 = str_1.replace(i, "")
print(str_1)