import java.io.*;

import java.util.*;

class Pair implements Comparable<Pair> {

public int l;

public int r;

Pair(int l, int r) {

this.l = l;

this.r = r;

}

@Override

public int compareTo(Pair pair) {

if (this.l > pair.l) {

return 1;

} else if (this.l < pair.l) {

return -1;

} else {

if (this.r > pair.r) {

return 1;

} else {

return -1;

}

}

}

}

public class Main {

public static void main(String[] args) throws IOException {

InputStreamReader isr = new InputStreamReader(System.in);

BufferedReader br = new BufferedReader(isr);

String line;

int n = Integer.parseInt(br.readLine());

while (n != 0) {

Pair[] blocks = new Pair[n];

// build an array of block pairs

for (int i = 0; i < n; i++) {

String[] tokens = br.readLine().trim().split("\\s+");

int l = Integer.parseInt(tokens[0]);

int r = Integer.parseInt(tokens[1]);

blocks[i] = new Pair(l, r);

}

// using the custom comparator

Arrays.sort(blocks);

// for (Pair p : blocks) {

// System.out.printf("%d %d\n", p.l, p.r);

// }

// System.out.println();

n = Integer.parseInt(br.readLine());

}

}

}