use std::cmp::*;
use std::collections::*;
use std::io::*;
use std::str::FromStr;
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}
fn main(){
    let s:String = read();
    if(s == "1" || s == "2"){
        println!("-1");
    }else{
        let mut n:Vec<char> = s.chars().collect();
        let mut dig = vec![0;10];
        for i in n{
          dig[(i as i32 - 48) as usize] += 1;
        }
        let mut k = 0;
        for i in dig{
            k = max(k,i);
        }
        match k{
            1 => println!("1"),
            _ => println!("-1"),
        }
    }
}