#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX 1001

void sort(char **arr, int n);
void swap(char **arr1, char **arr2);

int main(void) {
  int n;
  scanf("%d", &n);
  getchar();
  // 2d array
  char **str = malloc(sizeof(char *) * n);
  // Buffer array
  char *buffer = malloc(sizeof(char) * MAX);

  for (int i = 0; i < n; i++) {
    fgets(buffer, MAX, stdin);
    str[i] = malloc(strlen(buffer) + 1);
    strcpy(str[i], buffer);
  }

  sort(str, n);

  for (int i = 0; i < n; i++) {
    printf("%s", str[i]);
  }

  // Free up memory
  free(buffer);
  for (int i = 0; i < n; i++) {
    free(str[i]);
  }
  free(str);
  return 0;
}

void sort(char **arr, int n) {
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n - 1; j++) {
      if (strcmp(arr[j], arr[j + 1]) > 0) {
        // Why I can't use swap() here?
        char *tmp = arr[j];
        arr[j] = arr[j + 1];
        arr[j + 1] = tmp;
      }
    }
  }
}