N = int(input())
S = [input() for _ in range(N)]
ans = ''

while S:
    S.sort()
    l = [Si for Si in S if Si[0]==S[0][0]]
    
    for i in range(len(l)):
        if len(l[i])!=1:
            mark = i
            break
    else:
        mark = 0
    
    ans += S[mark][0]
    S[mark] = S[mark][1:]
    
    if S[mark]=='':
        S = [S[i] for i in range(len(S)) if i!=mark]
    
print(ans)