One day Xiao Ming is not happy because he has no idea about how to run out of his pocket money. At that moment, a mysterious man appears with a smile:"My keys are on sale, three yuan can buy a key, ten yuan can buy three keys.How many keys do you wanna buy?" 
Xiaoming is attracted by mysterious man and wants to spend all his money on buying keys. He doesn't want keep any money at the end. At the same time, because of the heavy weight of keys, Xiaoming Hopes that he can buy as few keys as possible. At the beginning, Xiao Ming had n yuan. Can you tell Xiaoming the minimum number of keys he can bought if he runs out of his pocket money?If Xiaoming can't run out of his money, please output "orz".