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