import java.util.Scanner;  
  
  
public class Main{  
  
public static void main(String[] args) {  
  
Scanner scan = new Scanner(System.in);  
long i,sum,n;  
while(scan.hasNextLong())  
{  
  
n = scan.nextLong();  
sum = 0;  
for(i=1; i<=n;i++)  
{  
sum = sum+i;  
}  
System.out.println(sum);  
System.out.print("\r\n");  
}  
}  
//java/8140