public class Rational {
   int n;  // numerator
   int d;  // denominator

   Rational(int numerator, int denominator) {
      n = numerator;
      d = denominator;
   }

   public int getNumer() {
      return n;
   }

   public int getDenom() {
      return d;
   }

   public Rational plus(Rational r2) {
      int n2 = r2.getNumer;
      int d2 = r2.getDenom;
      return(new Rational(n*d2 + n2*d, d*d2));
   }

   public Rational minus(Rational r2) {
      return plus(r2.negate());
   }

   public Rational times(Rational r2) {
      int n2 = r2.getNumer;
      int d2 = r2.getDenom;
      return(new Rational(n*n2, d*d2));
   }

   public Rational over(Rational r2) {
      return plus(r2.invert());
   }

   public Rational negate() {
      return (new Rational(-n, d));
   }

   public Rational invert() {
      return (new Rational(d, n));
   }

   public String toString() {
      return ("" + n + "/" + d);
   }
}