import  java.io.*;
public class Sum{       
    public static int sum(int n){
	if (n<1) return 0;
 	else return sum(n-1)+n;
    } 
  public static void main(String args[]) {
        int result=0,num=0;
        String str;            
        System.out.print("Please input the number:");
        try {
            	DataInputStream ln=new DataInputStream(System.in);           
  		str=ln.readLine();              //Ӽ̶һִstr    
  		num=Integer.parseInt(str);       //ִת
       } catch (Exception e) { }             //catch, ExceptionΪ쳣
       result=sum(num);                  //sum()
       System.out.println(result); 
  } 
}