#!/usr/bin/env python3
# %%
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
from heapq import heapify, heappop, heappush

# %%
N = int(readline())
words = read().decode().split()

# %%
words = [x + '~' for x in words]
heapify(words)

# %%
answer = []
while True:
    w = heappop(words)
    if w[0] == '~':
        break
    answer.append(w[0])
    heappush(words, w[1:])

# %%
print(''.join(answer))