#include <bits/stdc++.h>
using namespace std;
int main() {
  vector<int> v;
  vector<pair<long long int, long long int> > vi;
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int x, y, i, m = 1, h, cou = 0, a, n1, n2, j = 0, f = 0, k = 0, l,
                         arr[200005], arr2[10005];
  long long int n;
  cin >> n;
  for (i = 1; i <= n / 2; i++) k = k + i;
  k *= 2;
  if (n % 2 == 1) k += i;
  cout << k;
  return 0;
}
