#include <iostream>
#include <sstream>
#include <vector>
#include <array>
#include <string>
#include <algorithm>
#include <map>
#include <cmath>
#include <random>

using namespace std;

#define REP(i,first,last) for (int i=first;i<last;++i)
#define MAX(x,y) (x > y ? x : y)
#define MIN(x,y) (x < y ? x : y)

int N;

int main(){
  cin >> N;
  
  long max = 0;
  for (long i=0;i<N;i++) {
    long val = (i + 1) * (N - i) + i;
    max = MAX(val, max);
  }

  cout << max << endl;
}