n=int(input())
a=[]
for i in range(n):
  a.append([x if x!="-" else "nyanpass" for x in input().split()])
v=[]
for i in range(n):
  s=set()
  for j in range(n):
    s.add(a[j][i])
  if len(s)==1:
    v+=[j-1]
print(v[0] if len(v)==1 else -1)