/*
TASK:necklace
LANG:C++
*/
#include<iostream>
#include<cmath>
using namespace std;
int pr_chet=4, q, n, d=0,br=3,t=0,z=1;
int main()
{
	cin>>n;
	for(int i=5;i<=n;i++)
	{br=br+pr_chet;
    if(i%2==0) pr_chet=i; }
    cout<<br;
    return 0;
}
