import java.util.*;

public class Main {

    public static void main(String[] args) {

        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        System.out.println(n);


        for (int i = 0; i < 2*n; i++) {
            System.out.println(scan.next());
//            int nn = scan.nextInt();
//            System.out.println("nn = " + nn);
//            int [] ar = new int[nn];
//            int counter = 0;
//            String strAll = scan.next();
//            System.out.println("strAll = " + strAll);
//            for (String str: strAll.split(" ")) {
//                ar[counter] = Integer.parseInt(str);
//                counter++;
//            }
//            //System.out.println(ar);
//            String out = new Finder(nn, ar).find() + "";
//            System.out.println(out);
        }



    }

    public static class Finder {

        private int n;
        private int[] ar;

        public Finder(int n, int[] ar) {
            this.n = n;
            this.ar = ar;
        }
        public int find() {

            int sum = sum(ar);

            while (true) {
                int minInd = findMinIndex(ar);
                int maxInd = findMaxIndex(ar);
                ar[minInd]++;
                ar[maxInd]--;
                int newSum = sum(ar);
                if (newSum >= sum) {
                    return sum;
                }
                sum = newSum;
            }

        }

        private int sum (int[] ar) {
            int out = 0;
            for (int i = 0; i < ar.length; i++) {
                for (int ii = i; ii < ar.length; ii++) {
                    out = out + Math.abs(ar[i] - ar[ii]);
                }
            }
            return out;
        }

        private int findMinIndex(int[] ar) {
            int min = ar[0];
            int index = 0;
            for (int i = 0; i < ar.length; i++) {
                if (ar[i] < min) {
                    min = ar[i];
                    index = i;
                }
            }
            return index;
        }


        private int findMaxIndex(int[] ar) {
            int max = ar[0];
            int index = 0;
            for (int i = 0; i < ar.length; i++) {
                if (ar[i] > max) {
                    max = ar[i];
                    index = i;
                }
            }
            return index;
        }

    }





}
