#include<iostream>
using namespace std;
int main(){
 int n;
  cin>>n;
  int ans=0;
  for(int i=1;i<=n;i++){
    if(i<10 || (i>=100&&i<=999) || (i>=10000&&i<=99999))
      ans++;
  }
  cout<<ans;
}
### Prompt

Develop a solution in cpp to the problem described below:

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>
using namespace std;
int main(){
 int n;
  cin>>n;
  int ans=0;
  for(int i=1;i<=n;i++){
    if(i<10 || (i>=100&&i<=999) || (i>=10000&&i<=99999))
      ans++;
  }
  cout<<ans;
}
```