c#百钱买百鸡

int a, b, c;
            a = 70;
            b = 50;
            c = 3;
            int sum = 0;
            for (int i = 1; i < 20; i++)
            {
                for (int j = 1; j < 33; j++)
                {
                    for (int z = 1; z < 333; z++)
                    {
                        if ((a * i + b * j + z/3*10 ==1000)&&(z%3==0))
                        {
                            if (i + j + z == 100)
                            {
                                richTextBox1.AppendText("a b c=" + i.ToString() + " " + j.ToString() + " " + z.ToString() + "\n");
                                sum++;
                            }
                        }
                    }
                }
            }
            richTextBox1.AppendText("答案共 "+sum.ToString()+" 种");
            MessageBox.Show("完成! 答案共"+sum.ToString()+"种");