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 PyPy3 (2.4.0) (judge verdict: Runtime Error)

n,m=map(int,input().split())
ans=[set()for i in range(n)]
for i in range(m):
    s,c=map(int,input().split())    
    ans[s-1].add(c)
f=1
an=''
#print(ans)
for i in ans:
    if len(i)>1:
        f=0
        break
    if len(i)==0:
        an+='p'
    else:
        an+=str(i.pop())
if not f:
    print(-1)
else:
    an=an.replace('p','0')
    if an[0]=='0':
        print(-1)
    else:    
        print(an)