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

In Cpp, your task is to solve 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>
using namespace std;
int n,ans=0;
int main(void){
  cin>>n;
  for(int i=1;i<=n;i++)if(i<10||(i/100<10&&i>=100)||(i/10000<10&&i>=10000))ans++;
  cout<<ans;
  return 0;
}
```