# from pprint import pprint
# from icecream import ic

def main():
  N=int(input())
  S="nyanpass"
  a=[[] for i in range(N)]
  for i in range(N):
    a[i]=input().split()
  q=set()
  r=set(range(1,N+1))
  for i in range(N):
    for j in range(N):
      if i!=j and a[j][i]!=S:
        q.add(i+1)
  ans=r-q
  if len(ans)==1:
    for i in ans:
      print(i)
  else:
    print(-1)
if __name__=="__main__":
  main()