import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class Main {
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int N = Integer.parseInt(br.readLine());
int sum = 0;
for (int i = 1; i <= N; i++) {
sum += i;
}
System.out.println(sum);
br.close();
}
}