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

public class Hello {
	public static void main (String[] args) throws IOException {
		int n = 0;
		int ans = 0;

		InputStreamReader is = new InputStreamReader(System.in);
		BufferedReader br = new BufferedReader(is);

		String str = br.readLine();
		n = Integer.parseInt(str);

		for (int i = 1; i <= n; i++) {
			ans += i;
		}
		System.out.println(ans);
	}
}