#include<iostream>
using namespace std;
int main(){
  string tmp;
  int n,cnt=0;
  cin >>n;
  for(int i=1;i<=n;i++){
    tmp = to_string(i);
    if(tmp.size()%2==1) cnt++;
  }
  cout <<cnt <<endl;
}

### Prompt

Please formulate 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>
using namespace std;
int main(){
  string tmp;
  int n,cnt=0;
  cin >>n;
  for(int i=1;i<=n;i++){
    tmp = to_string(i);
    if(tmp.size()%2==1) cnt++;
  }
  cout <<cnt <<endl;
}

```