import sys import math import bisect from heapq import heapify, heappop, heappush from collections import deque, defaultdict, Counter from functools import lru_cache from itertools import accumulate, combinations, permutations, product sys.set_int_max_str_digits(10 ** 6) sys.setrecursionlimit(1000000) MOD = 10 ** 9 + 7 MOD99 = 998244353 input = lambda: sys.stdin.readline().strip() NI = lambda: int(input()) NMI = lambda: map(int, input().split()) NLI = lambda: list(NMI()) SI = lambda: input() SMI = lambda: input().split() SLI = lambda: list(SMI()) EI = lambda m: [NLI() for _ in range(m)] def main(): N = NI() S = [SI()+"|" for _ in range(N)] ans = [] while S: S.sort() ans.append(S[0][0]) S[0] = S[0][1:] if S[0] == "|": S.pop(0) print("".join(ans)) if __name__ == "__main__": main()