#include <iostream>
#include <string>
using namespace std;

int main(){

	int n,ans;
	cin >> n;
	ans =0;
	for(int i=1;i<=n;i++){
		if(to_string(i).length() % 2 == 1)ans++;
	}
	cout << ans << endl;

	return 0;
}
### Prompt

Generate 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>
#include <string>
using namespace std;

int main(){

	int n,ans;
	cin >> n;
	ans =0;
	for(int i=1;i<=n;i++){
		if(to_string(i).length() % 2 == 1)ans++;
	}
	cout << ans << endl;

	return 0;
}
```