#include <bits/stdc++.h>
using namespace std;
pair<int, int> a[10000];
int p[10000];
int main() {
  int n, c = 0;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    for (int j = 0; j <= n - i; j++) {
      a[c].first = j;
      a[c].second = j + i;
      c++;
    }
  }
  int res = 0;
  for (int i = c - 1; i >= 0; i--) {
    if (p[i]) {
      continue;
    }
    int l = a[i].first, r = a[i].second;
    for (int j = i; j >= 0; j--) {
      if (p[i]) {
        continue;
      }
      if (a[j].second == l) {
        l = a[j].first;
        p[j] = 1;
      }
      if (a[j].first == r) {
        r = a[j].second;
        p[j] = 1;
      }
    }
    p[i] = 1;
    res++;
  }
  cout << res;
}
