import sys
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def LI2(): return list(map(int,sys.stdin.readline().rstrip()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())
def LS2(): return list(sys.stdin.readline().rstrip())


N = I()
S = [S()+'{' for _ in range(N)]

ANS = []
while True:
    S.sort()
    if S[0] == '{':
        break
    ANS.append(S[0][0])
    new_S = [S[0][1:]]
    for s in S[1:]:
        new_S.append(s)
    S = new_S

ans = ''.join(ANS)
print(ans)