#include<iostream>
using namespace std;

int main(){
    int n;
    cin>>n;
    int ans=0;
    for(int i=1;i<=n;i++){
        string s=to_string(i);
        if((s.size())%2==1)ans++;
    } 
    cout<<ans<<endl;
}
### Prompt

Your challenge is to write 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>
using namespace std;

int main(){
    int n;
    cin>>n;
    int ans=0;
    for(int i=1;i<=n;i++){
        string s=to_string(i);
        if((s.size())%2==1)ans++;
    } 
    cout<<ans<<endl;
}
```