Find the hotel

  Summer again! Flynn is ready for another tour around. Since the tour would take three or more days, it is important to find a hotel that meets for a reasonable price and gets as near as possible!
  But there are so many of them! Flynn gets tired to look for any. It’s your time now! Given the <p_i, d_i> for a hotel h_i, where p_i stands for the price and d_i is the distance from the destination of this tour, you are going to find those hotels, that either with a lower price or lower distance. Consider hotel h₁, if there is a hotel h_i, with both lower price and lower distance, we would discard h1. To be more specific, you are going to find those hotels, where no other has both lower price and distance than it. And the comparison is strict.

There are some cases. Process to the end of file.
Each case begin with N (1 <= N <= 10000), the number of the hotel.
The next N line gives the (p_i, d_i) for the i-th hotel.
The number will be non-negative and less than 10000.

First, output the number of the hotel you find, and from the next line, print them like the input( two numbers in one line). You should order them ascending first by price and break the same price by distance.

3
15 10
10 15
8 9

1
8 9

ZSTU

HDU 2009-12 Programming Contest