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)

a=gets.chomp.split.map(&:to_i)
i=[]
a[0].times do 
  i.push(0)
end
i[0]=1
u=[]
m=0
a[1].times do 
  b=gets.chomp.split.map(&:to_i)
  if u.include?(b[0])==true&&i[b[0]-1]==b[1]
  elsif u.include?(b[0])==true
        m+=1
      puts -1
      break
  else i[b[0]-1]=b[1]
    u.push(b[0])
  end
end
1.times do
  if m!=0
    break
  end
if i[0]==0&&a[0]==1
  puts 0
  break
elsif i[0]==0
  puts -1
else puts i.join
end
end