#include<bits/stdc++.h>

using namespace std;

using ll = long long;
const int INF = 1<<30;
const long long LINF = 1LL<<60;
const long long MOD = (long long)1e9 + 7;

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