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")