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)

n, m = map(int, input().split())
x = [0] * m
y = [0] * m
r = [0] * n
for i in range(m):
    x[i], y[i] = map(int, input().split())
    if r[x[i] - 1] == 0 or r[x[i] - 1] == y[i]:
        r[x[i] - 1] = y[i]
if n > 1 and r[0] == 0:
    print(-1)
else:
    print(*r, sep='')