def conv(dl):
    res = ""
    cand = []
    for i,t in enumerate(dl):
        if t:
            a = chr(i+ord("a"))
            res += a
            cand.append(a)
    res += cand[0]
    return res

n = int(input())
dp = [[False]*26 for _ in range(n)]
cand = []

for i in range(n):
    ss = input()
    cand.append(ss)
    for si in ss:
        x = ord(si) - ord("a")
        dp[i][x] = True


for i in range(n):
    for j in range(26):
        if not dp[i][j]:
            c = [dp[k][j] for k in range(n) if k!=i]
            if all(c):
                ans = cand[i] + cand[i][0]
                print(ans)
                exit()
print("-1")