import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        
        Scanner scanner = new Scanner(System.in);
        
        float n = scanner.nextFloat();
        
        int sum = 0;
        
        for(int i=1;i<=n;i++){
            sum += i;
        }
        
        System.out.println(sum);
    }
    
}