import java.util.Scanner;
public class Main{
public static void main(String[] args){
int sum,n;
Scanner in=new Scanner(System.in);
while(in.hasNextInt()){
sum=0;
n=in.nextInt();
if(n==0){
System.out.println(sum);
System.out.println();
continue;
}
if(n%2==0)
sum=n/2*(n+1);
else
sum=(n+1)/2*n;
System.out.println(sum);
System.out.println();
}
}
}
