#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <map>
#include <set>
#include <algorithm>
#include <functional>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cctype>
#include <string>
#include <cstring>

using namespace std;

typedef long long ll;


int main() {
  ll n;
  cin >> n;
  if (n%2) {
    cout << max((n+1)/2-1+(n+1)/2*(n+1)/2, (n+1)/2+((n+1)/2+1)*((n+1)/2-1)) << endl;
  }else {
    cout << n/2+(n/2+1)*n/2 << endl;
  }
}