#define _GLIBCXX_DEBUG //遅い可能性がある 
#include <bits/stdc++.h>
#include<atcoder/all>
using namespace atcoder;
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define ALL(a) (a).begin(),(a).end() //lower_bound(ALL(a),x)
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<vector<int>>;

int INF = 100100100;

const vector<int> dx = {1, 0, -1, 0};
const vector<int> dy = {0, 1, 0, -1};

int main() {
    int n;
    cin >> n;
    ll m = (1+n)/2;
    ll ans = (1+m) * m / 2;
    cout << ans << endl;
    return 0;
}