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())
SC = set(sorted([tuple(map(int, input().split())) for _ in range(M)]))

ans = [-1] * N
for s, c in SC:
    if ans[s-1] == -1:
        ans[s-1] = c
if N >= 2:
    if ans[0] == -1 or ans[0] == 0:
        print(-1)
        exit()
kotae = ''
for a in ans:
    if a == -1:
        kotae += '0'
    else:
        kotae += str(a)
print(kotae)