n=int(input())

def f(I):
    ans=""
    for i in range(ord("a"),ord("z")+1):
        ans+=I[i]*chr(i)
    print(ans)
X=[]
for i in range(n):
    s=input()
    #S=[str(c) for c in s]
    D=[0]*200
    for j in s:
        D[ord(j)]+=1
    X.append(D)
X.sort()
X=[0]+X+[0]
Ans=[]
for i in range(1,n+1):
    if X[i+1]!=X[i] and X[i-1]!=X[i]:
        Ans.append(X[i])
for I in Ans:
    for i in range(ord("a"),ord("z")+1):
      fg=1
      for j in range(ord("a"),ord("z")+1):
        II=I[:]
        II[i]+=1
        if II[j]==0 or i==j:
            continue
        II[j]-=1
        if II in X:
            fg=0
      if fg:
        II=I[:]
        II[i]+=1
        f(II)
        exit()
print(-1)