n=int(input())
a=[[str(i) for i in input().split()] for i in range(n)]

count=[0 for i in range(n)]
for i in range(n):
    for j in range(n):
        if i!=j and a[i][j]!='nyanpass':
            count[j]+=1
judge=0
ans=-1
for i in range(n):
    if count[i]==0:
        judge+=1
        ans=i
if judge==1:
    print(ans+1)
else:
    print(-1)