n = int(input())
renchon = "nyanpass"
tab = [0 for _ in range(n)]
for _ in range(n):
    sli = input().split()
    for i in range(n):
        if sli == renchon:
            tab[i] += 1

res = max(tab)
if res == 0:
    print(-1)
else:
    print(res if tab.count(res) == 1 else -1)