#include<iostream>
using namespace std;
int main(){
int x,sam=0;
cin>>x;

while(x>0)
{int c=0;
int y=x;
    while(y>0)
    {
     c++;
     y/=10;
    }

if(c%2!=0)
    sam++;
x--;
}
cout<<sam;
return 0;}

### 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 main(){
int x,sam=0;
cin>>x;

while(x>0)
{int c=0;
int y=x;
    while(y>0)
    {
     c++;
     y/=10;
    }

if(c%2!=0)
    sam++;
x--;
}
cout<<sam;
return 0;}

```