#1858 RestMare

#include <iostream>
#include <fstream>
using namespace std;
ifstream in ("restmare.in");
ofstream out ("restmare.out");
long long int n,pana_unde,suma;
int main()
{
in >> n;
    if(n>2)
{

    if(n%2==1)
{        pana_unde = n/2;
suma = (pana_unde*(pana_unde+1))/2 + ((pana_unde-1)*pana_unde)/2;
  }
else
{
pana_unde = n/2-1;
  suma = pana_unde*(pana_unde+1);
  }
    }
    out << suma;
    return 0;}