function solve(input){

    let number = Number(input.shift());

      while(number !== undefined){
        let newnumber = Number(number);
        if(newnumber < 0){
            console.log("Negative number!");
            break;
        }else{
            newnumber = newnumber *2;
            console.log(newnumber.toFixed(2));
            number = input.shift();
        }
      }

}