#!/usr/bin/env python3

import heapq


def solve(n, ss):
    pq = [list(s + "{") for s in ss]
    heapq.heapify(pq)
    t = []
    for _ in range(sum(len(s) for s in ss)):
        s = heapq.heappop(pq)
        t += s.pop(0)
        heapq.heappush(pq, s)
    return "".join(t)


def main():
    n = int(input())
    ss = [input() for _ in range(n)]
    print(solve(n, ss))


if __name__ == '__main__':
    main()