#include<iostream>
#include<string>
using namespace std;
int main(){
	int k,t=0;cin>>k;for(int i=1;i<=k;i++) if(to_string(i).size()&1) t++;cout<<t;
}
### Prompt

Please provide a CPP coded solution 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>
#include<string>
using namespace std;
int main(){
	int k,t=0;cin>>k;for(int i=1;i<=k;i++) if(to_string(i).size()&1) t++;cout<<t;
}
```