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 Python (3.4.3) (judge verdict: Runtime Error)

import sys 
a = list(map(int,input().split()))

N = a[0]
M = a[1]

b = ['0']*N

for i in range(0,M):
    x = list(map(str,input().split()))
    if b[int(x[0])-1] != '0' and b[int(x[0])-1] != x[1]:
        print('-1')
        sys.exit()
    elif x[0] == '1' and x[1] == '0':
        print('-1')
        sys.exit()
    else:
        b[int(x[0])-1] = x[1]

if N == 2:
    if b[0] == '0' and int(b[1]) != 0:
        b[0] = '1'

if N == 3:
    if b[0] == '0' and (int(b[1]) != 0 or int(b[2]) != 0):
        b[0] = '1'
ans = ''.join(b)
print(ans)