public class Program

{

    public class Rational

    {  public int num;

     public int denum;

     public Rational(int num,int denum)

     { this.num=0;

      this.denum=1;

     }

        private static int NOD(int a,int b)

        {

            int x, r;

            if (a < b) { x = a; a = b; b = x; }

            while(b!=0)

            {

                r = a % b;

                a = b;

                b = r;

            }

            if (a >= 0) return a;

            else return -a;

        }

    public static Rational operator * (Rational r1,Rational r2)

        {

            Rational rezult = new Rational(0, 1);

            int n1 = r1.num * r2.num;

            int d1 = r1.denum * r2.denum;

            int s = NOD(n1, d1);

            n1 = n1 / s;

            d1 = d1 / s;

            return rezult;

        }

        public static Rational operator - (Rational r1, Rational r2)

        {

            Rational rezult = new Rational(0, 1);

            int n1 = r1.num * r2.denum-r2.num*r1.denum;

            int d1 = r1.denum * r2.denum;

            int s = NOD(n1, d1);

            n1 = n1 / s;

            d1 = d1 / s;

            return rezult;

        }

    }

}

​