//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");