import std.algorithm, std.array, std.container, std.range, std.bitmanip;
import std.numeric, std.math, std.bigint, std.random, core.bitop;
import std.string, std.regex, std.conv, std.stdio, std.typecons;

void main()
{
  auto n = readln.chomp.to!size_t;
  auto si = iota(n).map!(_ => readln.chomp).array;

  auto hi = si.heapify!((a, b) {
    if (a.length == 1 && a[0] == b[0])
      return true;
    else if (b.length == 1 && a[0] == b[0])
      return false;
    else if (a > b)
      return true;
    else
      return false;
  });
  auto s = "";

  while (!hi.empty) {
    auto a = hi.front;
    s ~= a[0];
    if (a.length == 1)
      hi.removeFront;
    else
      hi.replaceFront(a[1..$]);
  }

  writeln(s);
}