Problem:
Score : 100 points

Problem Statement

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?

Constraints

1≦N≦100

Input

The input is given from Standard Input in the following format:

N

Output

Print the necessary number of candies in total.

Sample Input 1

3

Sample Output 1

6

The answer is 1+2+3=6.

Sample Input 2

10

Sample Output 2

55

The sum of the integers from 1 to 10 is 55.

Sample Input 3

1

Sample Output 3

1

Only one child. The answer is 1 in this case.

Solution in Ruby (2.3.3) (judge verdict: Wrong Answer)

result = "-1 -1"
h = {}
words = gets.chomp.split('')
border = words.size / 2
words.each_with_index do |w,i|
  v = h[w]
  if v
    c = v[0] + 1
    v = h[w] = [c, v[1], i + 1]
  else
    c = 1
    v = h[w] = [1, i + 1, i + 1]
  end
  if c >= border
    result = "#{v[1]} #{v[2]}"
    break
  end
end

puts result