from collections import defaultdict
N = int(input())
dd = defaultdict(int)
for i in range(N):
    s = input()
    cnt = [0]*26
    for ss in s:
        cnt[ord(ss) - 97] += 1
    dd[tuple(cnt)] += 1

chimatagram = defaultdict(int)
for k, v in dd.items():
    cnt = list(k) # list化する
    for i in range(26):
        cnt[i] += 1
        chimatagram[tuple(cnt)] += v
        cnt[i] -= 1

# ちまたぐらむの中で生成数1のものがあればそれを答えとする

for k, v in chimatagram.items():
    if v == 1:
        ans = []
        # k = (0, 1, ..., 1)
        for i in range(26):
            for _ in range(k[i]):
                ans.append(chr(97 + i))
        exit(print(''.join(ans)))
print(-1)