N=int(raw_input())
A=[raw_input().split() for j in range(N)]
renchon=-1
for i in range(N):
    ok=True
    for j in range(N):
        if i==j:
            continue
        if A[j][i]!="nyanpass":
            ok=False
    if ok:
        if renchon!=-1:
            print -1
            exit()
        renchon=i+1
print renchon