import java.util.*;

public class Main {

    public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int l = Integer.parseInt(sc.next());
        String[] s = new String[n];
        for (int i = 0; i < n; i++) {
            s[i] = sc.next();
        }

        // 主処理
        Arrays.sort(s);
        String result = String.join("", s);

        // 出力
        System.out.println(result);
        sc.close();
    }
} import java.util.*; util.* java public class Main {

    public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int l = Integer.parseInt(sc.next());
        String[] s = new String[n];
        for (int i = 0; i < n; i++) {
            s[i] = sc.next();
        }

        // 主処理
        Arrays.sort(s);
        String result = String.join("", s);

        // 出力
        System.out.println(result);
        sc.close();
    }
} Main public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int l = Integer.parseInt(sc.next());
        String[] s = new String[n];
        for (int i = 0; i < n; i++) {
            s[i] = sc.next();
        }

        // 主処理
        Arrays.sort(s);
        String result = String.join("", s);

        // 出力
        System.out.println(result);
        sc.close();
    } main {

        // 入力
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int l = Integer.parseInt(sc.next());
        String[] s = new String[n];
        for (int i = 0; i < n; i++) {
            s[i] = sc.next();
        }

        // 主処理
        Arrays.sort(s);
        String result = String.join("", s);

        // 出力
        System.out.println(result);
        sc.close();
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = Integer.parseInt(sc.next()); n Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int l = Integer.parseInt(sc.next()); l Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc String[] s = new String[n]; s new String[n] n for (int i = 0; i < n; i++) {
            s[i] = sc.next();
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            s[i] = sc.next();
        } {
            s[i] = sc.next();
        } s[i] = sc.next() s[i] s i sc.next() sc.next sc Arrays.sort(s) Arrays.sort Arrays s String result = String.join("", s); result String.join("", s) String.join String "" s System.out.println(result) System.out.println System.out System System.out result sc.close() sc.close sc String args[] args public class Main {

    public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int l = Integer.parseInt(sc.next());
        String[] s = new String[n];
        for (int i = 0; i < n; i++) {
            s[i] = sc.next();
        }

        // 主処理
        Arrays.sort(s);
        String result = String.join("", s);

        // 出力
        System.out.println(result);
        sc.close();
    }
} public class Main {

    public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int l = Integer.parseInt(sc.next());
        String[] s = new String[n];
        for (int i = 0; i < n; i++) {
            s[i] = sc.next();
        }

        // 主処理
        Arrays.sort(s);
        String result = String.join("", s);

        // 出力
        System.out.println(result);
        sc.close();
    }
} Main
import java.util.*;

public class Main {

    public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int l = Integer.parseInt(sc.next());
        String[] s = new String[n];
        for (int i = 0; i < n; i++) {
            s[i] = sc.next();
        }

        // 主処理
        Arrays.sort(s);
        String result = String.join("", s);

        // 出力
        System.out.println(result);
        sc.close();
    }
}
