#include<iostream>
using namespace std;
int a,b,c,ans;
int main()
{
	cin>>a;
	for(int i=1;i<=a;i++)
	{
		c=0;
		b=i;
		while(b!=0)
		{
			b/=10;
			c++;
		}
		if(c%2==1)
			ans++;
	}
	cout<<ans<<endl;
}
### 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 a,b,c,ans;
int main()
{
	cin>>a;
	for(int i=1;i<=a;i++)
	{
		c=0;
		b=i;
		while(b!=0)
		{
			b/=10;
			c++;
		}
		if(c%2==1)
			ans++;
	}
	cout<<ans<<endl;
}
```