n=int(input())
a=[input().split() for i in range(n)]
ans=[]
for i in range(n):
  f=1
  for j in range(n):
    if i!=j:
      if a[j][i]!='nyapass':
        f=0
  if f==1:
    ans.append(i)
if len(ans)==1:
  print(ans[0]+1)
else:
  print(-1)