To chat or not to chat, it is a question. Zero is so angry because when he plays LOL, there is nobody plays with him. So, zero wants to punish them.
Now, the rule is that there are almost N men, everybody can play with others. But, if one of them who plays with M people, these M people can not play with each other
Now we agreed that one plays with another to be a playing relationship.
For example, if man A plays with man B, man C, man D, then man B can not play with man C and man D, of course the same as man C and man D. And there are three playing relationships.
There are N people, can you get the maximum number of playing relationships.

Input until EOF.
Each line contains one integer N(1 < N <= 10^9) means the number of people.

One line one output, print the maximum number of playting relationships.