codeforces 804A——Find Amir

A. 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 .

简单贪心。首先学校i和学校n+1-i肯定是免费的，那么两两成对，而相邻两队的价格为1，所以分奇偶讨论一下即可

#include<cstdio>#include<cstring>#include<queue>#include <cstdlib>#include<map>#include <set>#include <queue>#include <iostream>using namespace std;const int MAXN = 1000010;long long INF = 0x7fffffffffffffff;int main() {int n;cin >> n;if (n % 2 == 0) {cout << n / 2 - 1<< endl;}else {cout << n / 2 << endl;}}