import java.util.*;

public class Main {
    static final int MOD = 1000000007;
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long ans = 0;
        for (int i = 0; i <= n; i++) {
            ans += n - i + 1;
        }
        System.out.println(ans);
    }
}