public class Fraction
    {
        private int _numerator;
        private int _denominator;

        public Fraction() { }

        public int Numerator
        {
            get { return _numerator; }
            set { _numerator = value; }
        }

        public int Denominator
        {
            get { return _denominator; }
            set { _denominator = value; }
        }

        private void Reduce()
        {
            int gcd = GreatCommonDivisor(_numerator, _denominator);

            _numerator /= gcd;
            _denominator /= gcd;
        }

        public void SumUp(Fraction f)
        {
            int lcm = LeastCommonMultiple(_denominator, f.Denominator);

            int f1_Numerator = _numerator * (lcm / _denominator);
            int f2_Numerator = f.Numerator * (lcm / f.Denominator);

            _numerator = f1_Numerator + f2_Numerator;
            _denominator = lcm;

            Reduce();
        }

        private int GreatCommonDivisor(int a, int b)
        {
            int dividend, divisor, tmp;

            dividend = a > b ? a : b;
            divisor = a < b ? a : b;

            while (dividend % divisor != 0)
            {
                tmp = divisor;
                divisor = dividend % divisor;
                dividend = tmp;
            }

            return divisor;
        }

        private int LeastCommonMultiple(int a, int b)
        {
            int gcd, lcm;

            gcd = GreatCommonDivisor(a, b);
            lcm = (a / gcd) * (b / gcd) * gcd;

            return lcm;
        }

        public override string ToString()
        {
            return string.Format("{0}/{1}", _numerator, _denominator);
        }
    }