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)

s = gets.chomp.chars
abc = s.each_index.each_cons(3).find {|abc| abc.map{|i| s[i] }.uniq.size < abc.size }
if abc
    puts "%d %d" % abc.values_at(0,2).map{|i| i + 1}
elsif s.size < 3 && s.uniq.size < s.size
    puts "0 1"
else
    puts "-1 -1"
end