牙膏5元，牙刷2元，肥皂3元，100元买这三种恰好花光，请问有多少种可能性

           Console.WriteLine("牙膏5元，牙刷2元，肥皂3元，100元买这三种恰好花光");
            int a1 = 0, b1 = 0, c1 = 0, sum = 0;
            for (int a = 0; a <= 20; a++)
            {
                a1 = 5 * a;
                for (int b = 0; b <= 50; b++)
                {
                    b1 = 2 * b;
                    for (int c = 0; c < 33; c++)
                    {
                        c1 = 3 * c;

                        if (a1 + b1 + c1 == 100)
                        {
                            sum += 1;
                            Console.WriteLine("买牙膏"+a+"支，牙刷"+b+"支，肥皂"+c+"块！");
                        }
                    }
                }

            }
            Console.WriteLine("一共有"+sum+"种可能性！");