/* 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
{
	public static void main (String[] args) throws java.lang.Exception
	{
		// your code goes here
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int res = fun(n);
		System.out.println(res);
 
	}
 
	public static int fun(int n){
		if(n==0)
			return 0;  // now the process start of sending answer upward.
		return n + fun(n-1);
	}
}

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MTA=

10