import java.io.*;
public class No_480{
	public static void main(String args[]){
		try{
			BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
			int sum = 0;
			String sNumber = br.readLine();
			int number = Integer.parseInt(sNumber);
			if((1 <= number) && (number <= 100)){
				for(int i = 1; i <= number; i++){
					sum += i;
				}
				System.out.println(sum);
			}
		}catch(IOException e){}
	}
}