Problem:
Score : 100 points

Problem Statement

Takahashi wants to print a document with N pages double-sided, where two pages of data can be printed on one sheet of paper.

At least how many sheets of paper does he need?

Constraints

N is an integer.

1 \leq N \leq 100

Input

Input is given from Standard Input in the following format:

N

Output

Print the answer.

Sample Input 1

5

Sample Output 1

3

By printing the 1-st, 2-nd pages on the 1-st sheet, 3-rd and 4-th pages on the 2-nd sheet, and 5-th page on the 3-rd sheet, we can print all the data on 3 sheets of paper.

Sample Input 2

2

Sample Output 2

1

Sample Input 3

100

Sample Output 3

50

Solution in Ruby (2.3.3) (judge verdict: Runtime Error)

digit_number, requirements_count = gets.chomp.split(' ').map(&:to_i)

requirements = []
requirements_count.times do
  requirements << gets.chomp.split(' ').map(&:to_i)
end

result = Array.new(digit_number, 0)

f_flag = false


requirements.each do |req|
  target_index = req[0] - 1
  
  if (digit_number >= 2) && (target_index == 0) && req[1] == 0 
    f_flag = true
    break
  elsif  result[target_index] != 0  && result[target_index] != req[1] 
    f_flag = true
    break
  else
    result[target_index] = req[1]
  end
end

result[0] = 1 if digit_number >= 2 && result[0] == 0

if f_flag
  puts -1
else
  puts "#{result[0]}#{result[1]}#{result[2]}".to_i
end