#include <stdio.h>

int main(){
   int i,s = 0,n;
   scanf("%d",&n);
   for(i = 1;i <= n;i++){
      s = s + i;
   }
   
   printf("%d\n",s);
   return 0;
}

/**************************************************************
	Problem: 1002
	User: admin
	Language: C
	Result: Accepted
	Time:10 ms
	Memory:1144 kb
****************************************************************/