#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, mark[1000] = {0};
  cin >> n;
  mark[1] = 1;
  for (int i = (int)(2); i < (int)(n + 4); i++) {
    mark[i] = i + mark[i - 2];
  }
  cout << mark[n] << endl;
  return 0;
}
