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)]
S.sort()

ANS = []
while True:
    L = [[] for _ in range(26)]
    for s in S:
        L[ord(s[0])-97].append(s)
    for i in range(26):
        if L[i]:
            L[i].sort()
            ANS.append(L[i][0][0])
            new = []
            if len(L[i][0]) >= 3:
                new.append(L[i][0][1:])
            for s in L[i][1:]:
                new.append(s)
            for j in range(i+1,26):
                for s in L[j]:
                    new.append(s)
            S = new
            break
    else:
        break

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