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