CF-805C

C. Find Amir

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

A few years ago Sajjad left his school and register to another one due to security reasons. Now he wishes to find Amir, one of his schoolmates and good friends.

There are n schools numerated from 1 to n. One can travel between each pair of them, to do so, he needs to buy a ticket. The ticker between schools i and j costs  and can be used multiple times. Help Sajjad to find the minimum cost he needs to pay for tickets to visit all schools. He can start and finish in any school.

Input

The first line contains a single integer n (1 ≤ n ≤ 105) — the number of schools.

Output

Print single integer: the minimum cost of tickets needed to visit all schools.

Examples

input

2

output

0

input

10

output

4

Note

In the first example we can buy a ticket between the schools that costs .

题意：

共有n间学校，往返i，j两学校之间的票的价格为（i+j）%（n+1）。

求最小遍历所有学校的花费。

当n为偶数时，最小花费为n/2-1

1~n为0，n~2为1,2~n-1为0，以此类推。

当n为奇数时，需要连接中间的值，故再加一，为n/2.

附AC代码：

 #include<bits/stdc++.h>
 using namespace std;

 int main(){
     int n,ans=;
     cin>>n;
     if(n%){
         ans=n/;
     }
     else{
         ans=n/-;
     }
     cout<<ans<<endl;
     return ;
 }