代码

import java.io.BufferedReader;  
import java.io.IOException;  
import java.io.InputStreamReader; 

public class main{
    public static void main(String[] args) throws IOException,NumberFormatException{
    	BufferedReader s=new BufferedReader(new InputStreamReader(System.in));
        long n = Integer.parseInt(s.readLine());
    	long sum = (1+n)*n/2;
    	System.out.println(sum);
    }
}