use std::collections::HashSet;
use std::process;

fn getline() -> String{
	let mut __ret=String::new();
	std::io::stdin().read_line(&mut __ret).ok();
	return __ret;
}

fn main() {
	let S=getline();
	let S=S.trim();

	if S.len() == 1 {
		print!("{}", -1);
		process::exit(0);
	}

	let rev:String = S.chars().rev().collect();
		if S != rev {
			print!("{}", S.len());
			process::exit(0);
		}

	if S.len() == 2 {
		print!("{}", -1);
		process::exit(0);
	}

	let char_set: HashSet<_> = S.chars().collect();
	let char_num = char_set.len();

	if char_num == 1 {
		print!("{}", -1);
		process::exit(0);
	}

	if S.len() % 2 == 0 {
		print!("{}", S.len() -2);
		process::exit(0);
	}else {
		let mS = format!("{}{}", &S[..S.len()/2], &S[S.len()/2+2..]);
		let m_char_set: HashSet<_> = mS.chars().collect();
		let m_char_num = m_char_set.len();
		if m_char_num == 1 {
		print!("{}", S.len() -2);
		process::exit(0);
		}else {
		print!("{}", S.len() -2);
		process::exit(0);
		}
	}
}