c# while穷举（凑钱）

//1元，2元，5元；凑够20元有多少种可能

int x = 0, y = 0, z = 0, m = 0;

               while (x <= 20)
               {

                   while (y <= 10)
                   {

                       while (z <= 4)
                       {

                           if (x + 2 * y + 5 * z == 20)
                           {
                               Console.WriteLine(x + "," + y + "," + z);
                               m++;
                           }
                           z++;
                       }
                       y++;
                       z = 0;
                   }
                   y = 0;
                   x++;

               }
               Console.WriteLine("总共有" + m + "种可能");