text: /*numPass=1, numTotal=6
  Verdict:WRONG_ANSWER, Visibility:1, Input:"2", ExpOutput:"4", Output:"6"
  Verdict:WRONG_ANSWER, Visibility:1, Input:"4", ExpOutput:"20", Output:"15"
  Verdict:WRONG_ANSWER, Visibility:1, Input:"10", ExpOutput:"220", Output:"66"
  Verdict:ACCEPTED, Visibility:1, Input:"3", ExpOutput:"10", Output:"10"
  Verdict:WRONG_ANSWER, Visibility:0, Input:"1", ExpOutput:"1", Output:"3"
  Verdict:WRONG_ANSWER, Visibility:0, Input:"20", ExpOutput:"1540", Output:"231"
  */
  #include<stdio.h>
  
      int main() {
      int i,n,T=0;
      
      scanf("%d",&n);
      
      for (i=0;i<=n;i=i+1);
          
      T=T+(i*(i+1)/2);
      
      printf("%d",T);
      
      return 0;
  }