/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	static int sum(int n)
	{
		if(n==0)
		return 0;
		if(n==1)
		return 1;
		else 
		return n+sum(n-1);
	}
	public static void main (String[] args) throws java.lang.Exception
	{
		// your code goes here
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		System.out.println(sum(n));
	}
}

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Mw==

3