#!/usr/bin/python3

N = int(input())

S = []

cnt = 0

for i in range(N):
    S.append(input()+"{")

T = ""

while True:
    mi = ['-']*2
    for i in range(N):
        if len(S[i]) == 0:
            continue

        if mi[0] == '-':
            mi[0] = S[i]
            mi[1] = i

        if mi[0] > S[i]:
            mi[0] = S[i]
            mi[1] = i

    if mi[0] == '-':
        break
    T += mi[0][0]
    S[mi[1]] = S[mi[1]][1:]

print(T[0:len(T)-len(S)])