Problem:
Score : 200 points

Problem Statement

Given is an integer N. Find the number of positive integers less than or equal to N that have an odd number of digits (in base ten without leading zeros).

Constraints

1 \leq N \leq 10^5

Input

Input is given from Standard Input in the following format:

N

Output

Print the number of positive integers less than or equal to N that have an odd number of digits.

Sample Input 1

11

Sample Output 1

9

Among the positive integers less than or equal to 11, nine integers have an odd number of digits: 1, 2, \ldots, 9.

Sample Input 2

136

Sample Output 2

46

In addition to 1, 2, \ldots, 9, another 37 integers also have an odd number of digits: 100, 101, \ldots, 136.

Sample Input 3

100000

Sample Output 3

90909

Solution in Python (3.4.3) (judge verdict: Accepted)

#B
n = int(input())
s = str(n)
l = len(s)

cnt = 0

for i in range(1,l+1):
    s = str(n)
    l = len(s)
    if i % 2 == 1:
        if n < 10:
            cnt += n
            break
        elif i == 1:
            cnt += 9
            
        elif n < 10**i:
            cnt += n - 10**(i-1) + 1
            
            
        else:
            cnt += 10**(i) - 10**(i-1)
print(cnt)