N=int(input())
S=[[ord(s)-97 for s in input()] for i in range(N)]
C=[[0]*26 for i in range(N)]
for i in range(N):
    for s in S[i]:
        C[i][s]+=1
for i in range(N):
    for a in range(26):
        T=S[i]+[a]
        cnt=[0]*26
        for t in T:
            cnt[t]+=1
        for j in range(N):
            if i==j:
                continue
            if all(C[j][b]<=cnt[b] for b in range(26)) and sum(cnt)>=sum(C[j]):
                break
        else:
            ans=""
            for a in range(26):
                ans+=chr(a+97)*cnt[a]
            print(ans)
            exit()
print(-1)