n=int(input())
a=[list(input().split()) for _ in range(n)]
b=[]
for i in range(n):
    ok=True
    for j in range(n):
        if a[j][i]!='nyanpass' and i!=j:
            ok=False
    if ok:
        b.append(i+1)
if len(b)==1:
    print(b[0])
else:
    print(-1)