import java.util.*;import java.io.*;public class Main{static int [] dp = new int [1010];public static void main(String [] args)throws IOException{Mouse [] mice = new Mouse [1010];FileReader fr=new FileReader("in.txt");   //讀取文件BufferedReader read = new BufferedReader(fr);String str = "";int n=1;while((str = read.readLine())!=null){String [] s= str.split(" ");mice[n] = new Mouse();   //對象實例化，很重要mice[n].weight = Integer.parseInt(s[0]);mice[n].speed =Integer.parseInt(s[1]);n++;}System.out.PRintln(n);Arrays.sort(mice,1,n);   //sort(int start,int end)  包括start索引，不包括end索引for(int i=1;i<n;i++){System.out.println(mice[i].weight+" "+mice[i].speed);}}}class Mouse implements Comparable{   //實現Comparable接口int weight;int speed;public int compareTo(Object o){     //重寫compareTo方法Mouse m=(Mouse)o;return weight>m.weight?1:(weight==m.weight?0:-1);}}