N = int(input())
S = []
for _ in range(N):
   s = input()
   s = "".join(sorted(s))
   S.append(s)

from collections import Counter

C = Counter()
for s in S:
   for i in range(len(s)):
      u = s[:i] + s[i+1:]
      C[u] += 1

for u, cnt in C.items():
   if cnt == 1:
      break
else:
   print(-1)
   exit()

target = u

for s in S:
   for i in range(len(s)):
      u = s[:i] + s[i+1:]
      if u == target:
         break

print(s + "x")