There are N children in AtCoder Kindergarten. Mr. Evi will arrange the children in a line, then give 1 candy to the first child in the line, 2 candies to the second child, ..., N candies to the N-th child. How many candies will be necessary in total?
N=int(input())

i=0

for i in range(N):
  i+=1
  
a = int(input())

print(int(a*(a+1)/2))