count = {}
string = input()
for letter in string:
    if letter.isdigit():
        count[letter] = count.get(letter, 0) + 1
res = ''
min_num_odd = None
start_num = None
for num in sorted(count.keys()):
    if min_num_odd is None and count[num] % 2 == 1:
        min_num_odd = num
    if start_num is None and count[num] > 1 and num != '0':
        start_num = num
        count[num] -= 2
    res += num * (count[num] // 2)
if start_num is None and min_num_odd is None:
    print(0)
elif start_num is None:
    print(min_num_odd if count.get('0', 0) == 0 else 0)
elif min_num_odd is None:
    print(start_num, res, res[::-1], start_num, sep='')
else:
    print(start_num, res, min_num_odd, res[::-1], start_num, sep='')