#include <iostream>
#include <algorithm>

int main()
{
  int n;
  int r=0;
  std::cin>>n;
  int a=1;
  while(a<=n){
    r+=std::min(a*10, n+1)-a;
    a*=100;
  }
  std::cout<<r;
  return 0;
}

### Prompt

Generate a cpp solution to the following problem:

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.

Examples

Input

11


Output

9


Input

136


Output

46


Input

100000


Output

90909

### Response

```cpp
#include <iostream>
#include <algorithm>

int main()
{
  int n;
  int r=0;
  std::cin>>n;
  int a=1;
  while(a<=n){
    r+=std::min(a*10, n+1)-a;
    a*=100;
  }
  std::cout<<r;
  return 0;
}

```