import java.io.*;
import java.util.*;

class Main
{
    public static void main(String args[])throws Exception
    {
        BufferedReader bu=new BufferedReader(new InputStreamReader(System.in));
        StringBuilder sb=new StringBuilder();
        char s[]=bu.readLine().toCharArray();
        int i,c[]=new int[26],n=s.length;
        boolean p=true;
        for(i=0;i<n;i++)
        {
            c[s[i]-'a']++;
            p&=s[i]==s[n-i-1];
        }

        int ans,max=0;
        for(i=0;i<26;i++)
        if(c[i]!=0) max=Math.max(max,c[i]);

        if(!p) ans=n;
        else
        {
            if(max==n)
            {
                if(n%2==0) ans=0;
                else ans=-1;
            }
            else if(max==n-1) ans=-1;
            else ans=n-2;
        }
        System.out.println(ans);
    }
}