<a target=_blank href="http://acm.hdu.edu.cn/showproblem.php?pid=1001">杭电P1001</a>
import java.util.*;
class Main{
public static void main(String srgs[]){
Scanner sc =new Scanner (System.in);
while(sc.hasNext()){
int n=sc.nextInt();
int sum=0;
for(int i=1;i<=n;i++){
sum+=i;
}
System.out.println(sum);
System.out.println();
}
}
}