#include<iostream>
using namespace std;
int main(){
  int N;
  cin>>N;
  int count=0;
  for(int i=1; i<=N; i++){
    if(to_string(i).length()%2!=0) count++;
  }
  cout<<count<<endl;
  return 0;
}
### 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>
using namespace std;
int main(){
  int N;
  cin>>N;
  int count=0;
  for(int i=1; i<=N; i++){
    if(to_string(i).length()%2!=0) count++;
  }
  cout<<count<<endl;
  return 0;
}
```