n=int(input())
a=-1
is_renchon=[True]*n
for i in range(n):
    for (j,s) in enumerate(input().split()):
        if i==j:
            continue
        if s!="nyanpass":
            is_renchon[j]=False

a=-1
for i in range(n):
    if is_renchon[i]:
        if a==-1:
            a=i+1
        else:
            print(-1)
            exit()
print(a)