等差數列算法

	public static void main(String[] args) throws NumberFormatException, IOException {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        String message=null;
        while((message=br.readLine())!=null){
            int n=Integer.parseInt(message);
            int res=n*2+n*(n-1)*3/2;
            System.out.println(res);
        }
    }