CF411div2C.Find Amir

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.

题目大意： 1-n个城市 每个城市走一边  找出一条路线 使得路线   之和最小  

方案 从1走到n n走到2 2走到n-1 n-1走到3 3走到n-2 依次这样走  没走两步结果加一

 #include<iostream>using namespace std;int n;int main(){ cin>>n; cout<<(n+1)/2-1; return 0; }