/* -*- coding: utf-8 -*-
 *
 * 1617.cc:  No.1617 Palindrome Removal - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 1000000;

/* typedef */

/* global variables */

char s[MAX_N + 4];
int cs[26];

/* subroutines */

bool palindrome(int n, char s[]) {
  for (int i = 0, j = n - 1; i < j; i++, j--)
    if (s[i] != s[j]) return false;
  return true;
}

/* main */

int main() {
  scanf("%s", s);
  int n = strlen(s);

  if (! palindrome(n, s)) { printf("%d\n", n); return 0; }

  int k = 0;
  for (int i = 0; s[i]; i++)
    if (cs[s[i] - 'a']++ == 0) k++;

  if (k == 1 || n <= 3)
    printf("%d\n", (n & 1) ? -1 : 0);
  else
    printf("%d\n", n - 2);
  return 0;
}