#include <bits/stdc++.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define all(s) (s).begin(), (s).end()
#define rall(s) (s).rbegin(), (s).rend()
#define rep(i,l,r) for(int i=l;i<r;i++)
#define rrep(i,r,l) for(int i=r;i>l;i--)

using ll=long long;
using mint=modint998244353;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    ll N;cin>>N;
    ll k=N/2;
    cout<<-k*k+N*k+N<<endl;
}