#include <iostream>

int main(void){
  int i,s,a;
  std::cin>>a;
  s=0;
  
  for(i=10;i<=a;i*=100){
    s+=i-i/10;
  }
  
  if(a-i/10>=0)
    s+=a-i/10+1;
  
  std::cout<<s;
  
  return 0;
}

### Prompt

Create a solution in Cpp for 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>

int main(void){
  int i,s,a;
  std::cin>>a;
  s=0;
  
  for(i=10;i<=a;i*=100){
    s+=i-i/10;
  }
  
  if(a-i/10>=0)
    s+=a-i/10+1;
  
  std::cout<<s;
  
  return 0;
}

```