cf 328div 2 B. The Monster and the Squirrel

http://codeforces.com/contest/592/problem/B

B. The Monster and the Squirrel

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

Ari the monster always wakes up very early with the first ray of the sun and the first thing she does is feeding her squirrel.

Ari draws a regular convex polygon on the floor and numbers it's vertices 1, 2, ..., n in clockwise order. Then starting from the vertex 1she draws a ray in the direction of each other vertex. The ray stops when it reaches a vertex or intersects with another ray drawn before. Ari repeats this process for vertex 2, 3, ..., n (in this particular order). And then she puts a walnut in each region inside the polygon.

Ada the squirrel wants to collect all the walnuts, but she is not allowed to step on the lines drawn by Ari. That means Ada have to perform a small jump if she wants to go from one region to another. Ada can jump from one region P to another region Q if and only if P and Qshare a side or a corner.

Assuming that Ada starts from outside of the picture, what is the minimum number of jumps she has to perform in order to collect all the walnuts?

Input

The first and only line of the input contains a single integer n (3 ≤ n ≤ 54321) - the number of vertices of the regular polygon drawn by Ari.

Output

Print the minimum number of jumps Ada should make to collect all the walnuts. Note, that she doesn't need to leave the polygon after.

Sample test(s)

input

5

output

9

input

3

output

1

大意：

有n个点，1,2,3.....n顺时针排列围一个圈，从1点向其他n-1个点连线，规则是，如果画线时遇到先前的线则停止，遇到点 也停止，第 2,3，..n个点 也是如此画下去，问最后可以形成多少个区域；；；

画一画就发现规律了

代码超级短

#include <iostream>

using namespace std;

int main()
{
    long long n;
    while(cin>>n)
    {
        cout<<(n-1)*(n-3)+1<<endl;
    }
    return 0;
}