// use std::fmt::Write;
use std::collections::btree_map::BTreeMap;

type INT = u64;

pub fn main() {
    let buf_size: usize = 1000000;
    let mut input = String::with_capacity(buf_size);
    // let mut output = String::with_capacity(buf_size);
    std::io::stdin().read_line(&mut input).unwrap();
    input.pop();
    let n = input.len();
    let mut odd_count: i64 = 0;
    let mut middle = '#';
    let mut alphabet: BTreeMap<char, INT> = BTreeMap::from
        ([('A', 0), ('B', 0), ('C', 0), ('D', 0), ('E', 0), ('F', 0),
            ('G', 0), ('H', 0), ('I', 0), ('J', 0), ('K', 0), ('L', 0),
            ('M', 0), ('N', 0), ('O', 0), ('P', 0), ('Q', 0), ('R', 0),
            ('S', 0), ('T', 0), ('U', 0), ('V', 0), ('W', 0), ('X', 0),
            ('Y', 0), ('Z', 0)]);

    for c in input.chars() {
        *alphabet.entry(c).or_insert(0) += 1;
    }

    for (_, v) in &alphabet {
        if v % 2 != 0 { odd_count += 1 }
    }

    if odd_count > 1 {
        println!("NO SOLUTION");
        return;
    }
    if n == 1 {
        for (c, v) in alphabet {
            if v == 1 {
                println!("{}", c);
            }
        }
        return;
    }
    if n % 2 == 1 {
        for (c, v) in alphabet {
            if v % 2 == 1 {
                middle = c;
            }
        }
    }
    for (_, mut v) in alphabet.clone() {
        v = v / 2;
    }

    println!("{}", input.len());
}