class Main {
    
    public static void main(String[] args) {
        
        int n = Integer.parseInt(args[0]);
        
        String outStr = String.valueOf(sum(n));
        
        System.out.println(outStr);
        
    }
    
    public static int sum(int n) {
        int result = (1 + n) * n / 2;
        return result;
    }
    
}