if(s.length%2 !== 0){ return -1; }
    let sub = s.substring(0, s.length * 0.5).split(``);

    for(let i = sub.length; i < s.length; i++){
        let id = sub.indexOf(s.charAt(i));
        
        if(id !== -1){
            sub.splice(id,1);
        }
    }
    return sub.length;