Codeforces805 C. Find Amir 2017-05-05 08:41 140人阅读 评论(0) 收藏

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 .

——————————————————————————————————————

题目的意思是给出n要求遍历1~n，遍历是可以任意移动，从i移动到j花费（i+j）%

（n+1），问最小花费

思路，贪心尽可能凑n+1，我们可以很清楚发现1和n凑2和n-1凑，这样走都不用花费

，而他们之间转化两两之间最小花费1，n走到2，n-1走3，所以偶数个需走n/2-1，奇数

走n/2，合并起来就是（n-1）/2

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <vector>
using namespace std;
#define inf 0x3f3f3f3f
#define LL long long
 
int main()
{
    int n;
    scanf("%d",&n);
    printf("%d\n",(n-1)/2);
    return 0;
}