import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {
    public static void main(String... args) throws Exception {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        int N = Integer.parseInt(reader.readLine());
        int sum = 0;
        for (int i = 1; i <= N; i++) {
            sum += i;
        }
        System.out.println(sum);
    }
}