//No.71 そろばん

import java.util.*;
import java.io.*;
import static java.util.Arrays.*;
import static java.lang.Math.*;

public class No0071 {
    
    static final Scanner in = new Scanner(System.in);
    static final PrintWriter out = new PrintWriter(System.out,false);

    static void solve() {
        int n = in.nextInt();
        long max = 0;
        for (long i=0; i<=n; i++) {
            max = max(max,i+(i+1)*(n-i));
        }
        out.println(max);
    }

    public static void main(String[] args) {
        long start = System.currentTimeMillis();

        solve();
        out.flush();

        long end = System.currentTimeMillis();
        //trace(end-start + "ms");
        in.close();
        out.close();
    }

    static void trace(Object... o) { System.out.println(deepToString(o));}
}