#include<iostream>
#include<algorithm>
using namespace std;
int main(){
	int N,k,pre,sum=0;
	cin>>N;
	for(int i=1;i<=N;i++){
		k=0;pre=i;
		while(pre>0){k++;pre/=10;}
		sum+=k%2;
	}
	cout<<sum;
}
### 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>
#include<algorithm>
using namespace std;
int main(){
	int N,k,pre,sum=0;
	cin>>N;
	for(int i=1;i<=N;i++){
		k=0;pre=i;
		while(pre>0){k++;pre/=10;}
		sum+=k%2;
	}
	cout<<sum;
}
```