#include <vector>
#include <string>
#include <algorithm>
#include <numeric>
#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <utility>
#include <list>
#include <functional>
#include <queue>
#include <map>
#include <iterator>
#include <iomanip>
#include <complex>
using namespace std;

using ull = unsigned long long;
using ll = long long;


int main()
{
  ll L;
  cin >> L;

  ll count = 0;
  for(int i = 3; i <= L; i+=2)
  {
    count += L - i + 1;
  }

  cout << count << endl;
}