class Main{
	public static void main(String[] args){
		int total = 0;
		if(args.length > 0){
		  int cnt = Integer.parseInt(args[0]);
		  for(int i=0;i<=cnt;i++){
		  	total += i;
		  }
		}
		System.out.print(String.valueOf(total));
		System.out.print(args[0]);
	}
}