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 Python (3.4.3) (judge verdict: Wrong Answer)

s = input()

s_set = set( s )
target_ch = ''
for s_each in s_set :
	count = s.count( s_each )
	if count >= len(s)/2:
		target_ch = s_each
		break

if target_ch == '':
	print( "-1 -1" )
else:
	print( str( s.find( target_ch )+1 ) \
		+ " " \
		+ str( s.rfind( target_ch )+1 ) )