#coding:utf-8

def main():

	N=input()
	S=[raw_input().split() for i in range(N)]

	cnt=[]
	for i in S:
		for u in range(N):
			if i[u]=='nyanpass':
				cnt.append(u+1)
	
	ans={}		
	for i in sorted(set(cnt)):
		ans[i]=cnt.count(i)
	
	res=[]
	for i in ans.keys():
		if ans[i]==N-1:
			res.append(i)

	if len(res)==1:
		return res[0]
	else:
		return -1
	
if __name__=='__main__':
	print main()