#include <stdio.h>
int main()
{
    int N,i,candies=0;
     scanf("%d",&N);
       if(N>=1 && N<=100)
       {
       for(i=1;i<=N;i++)
        {
            candies = candies+i;
        }
       }
          printf("%d\n",candies);
    return 0;
}