#include<stdio.h>
int main()
{
int n,sum;
while(scanf("%d",&n)!=EOF)
{
if(n%2==0)
sum=n/2*(n+1);
else
sum=(n+1)/2*n;
printf("%d\n\n",sum);
}
return 0;
}
#include<stdio.h>
int main()
{
int n,sum;
while(scanf("%d",&n)!=EOF)
{
if(n%2==0)
sum=n/2*(n+1);
else
sum=(n+1)/2*n;
printf("%d\n\n",sum);
}
return 0;
}