def conv(dl):
    res = ""
    for i,t in enumerate(dl):
        if t:
            a = chr(i+ord("a"))
            res += a*2
    return res

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

for i in range(n):
    for si in input():
        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 = conv(dp[i])
                print(ans)
                exit()
print("-1")