#![allow(unused_imports)]
use std::cmp::*;
use std::collections::*;
use std::io::Write;
use std::ops::Bound::*;

#[allow(unused_macros)]
macro_rules! debug {
    ($($e:expr),*) => {
        #[cfg(debug_assertions)]
        $({
            let (e, mut err) = (stringify!($e), std::io::stderr());
            writeln!(err, "{} = {:?}", e, $e).unwrap()
        })*
    };
}

fn main() {
    let s = read::<String>().chars().collect::<Vec<_>>();
    if s.iter().all(|&x| x == s[0]) {
        if s.len() % 2 == 1 {
            println!("-1");
        } else {
            println!("0");
        }
        return;
    }
    if s.len() == 3 && s[0] == s[2] {
        println!("-1");
        return;
    }
    if (0..s.len()).all(|i| s[i] == s[s.len() - 1 - i]) {
        println!("{}", max(s.len() as i64 - 2, 0));
        // println!("-1");
        return;
    }
    println!("{}", s.len());
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}