import java.util.;
public class Main
{
public static void main(String[] args)
{
Scanner input=new Scanner(System.in);
int n=input.nextInt();
int ans=0;
for(int i=1;i<=n;i++)
{
int x=i;
int num=1;
while(x!=0)
{
num=x;
x–;
}
ans+=num;
}
System.out.println(ans);
}
}
