#include<stdio.h>
int main()
{int i,n;
int s=0;
scanf("%d",&n);
for(i=n;i>0;i--)
{s=s+i;} 
printf("%d",s);
return 0;
 } 
/**************************************************************
	Problem: 2100
	User: admin
	Language: C
	Result: Accepted
	Time:52 ms
	Memory:1144 kb
****************************************************************/