import java.util.Scanner;

class Main {
    
    public static int returnSum (int in) {
        int sum = 0;
        for (int i = 1; i <= in; i++){
            sum += i;
        }
        return sum;
    }
    
    public static void main (String[] args) {
        Scanner scan = new Scanner(System.in);
        
        int sum = returnSum(scan.nextInt());
        
       System.out.println(sum);
    }
}