shil-and-palindrome

Shil is your new boss and he likes palindromes very much.  Palindrome is a string that can be read the same way in either direction, from the left to the right and from the right to the left. (ex. madam , aabaa, racecar)  

Given a string S , beautiful Palindrome is a lexicographical minimum palindrome that can be formed by rearranging all the characters of string S. In order to please your boss, find a beautiful Palindrome that can be formed with help of string S.  

String x is lexicographically less than string y, if either x is a prefix of y (and x ≠ y), or there exists such i (1 ≤ i ≤ min(|x|, |y|)), that xi < yi, and for any j (1 ≤ j < i) xj = yj. Here |a| denotes the length of the string a. The lexicographic comparison of strings is implemented by operator < in modern programming languages​​.

Input:
Only line of input contains string S. All the letters of this string will be in lower letters('a' - 'z').

Output:
Output lexicographical minimum Palindrome that can be formed by rearranging all the letters of string S. If no such Palindrome exist for given  input, print -1.

Constraints: 
1≤|S|≤100000

SAMPLE INPUT
aabcc

SAMPLE OUTPUT
acbca

Explanation

After rearranging all the characters , all the palindromes that can be formed are cabac and acbca. Out of these two lexicographical minimum one is acbca.

Source: hackerearth | Difficulty: EASY
Tags: Fundamentals


Solutions:
s = input()
alphabet = [chr(i + ord('a')) for i in range(26)]
f = dict(list(zip(alphabet, [0]*26)))
for c in s: f[c] += 1
output = ''
for c in alphabet:
	while f[c] > 1:
		output += c
		f[c] -= 2
mid = []
for k, v in f.items():
	if v == 1:
		mid.append(k)
if len(mid) > 1:
	print(-1)
else:
	print(output + ''.join(mid) + output[::-1])