n = int(input())
ss = [list(input()) for _ in range(n)]


def is_timataguramu(s, t):
    kind = 0
    cnt = 0
    for i in range(26):
        if s[i] > t[i]:
            return False
        if s[i] == t[i]:
            continue

        kind += 1
        cnt += t[i] - s[i]

    return kind == 1 and cnt == 1


cnts = [[0] * 26 for _ in range(n)]
for i in range(n):
    for si in ss[i]:
        cnts[i][ord(si) - ord("a")] += 1

for i in range(n):
    for j in range(26):
        cnts[i][j] += 1
        ok = True
        for k in range(n):
            if i == k:
                continue

            if is_timataguramu(cnts[k], cnts[i]):
                ok = False

        if ok:
            ans = ""
            for l in range(26):
                ans += chr(l + ord("a")) * cnts[i][l]
            print(ans)
            exit()

        cnts[i][j] -= 1

print(-1)