public class Number {
  public double val; 
  public Number(double d) {
    val = d;
  }
  public Number op-=(double d) {
    return new Number(val - d);
  }
  public String toString() { return ""+val; }
  public static void main(String[]args) {
    Number n1 = new Number(1.0);
    double d = 10.0;
    System.out.println(n1 -= d);
  }
}