#include <iostream>
using namespace std;

int main() {
	int n;
	cin >> n;
	int answer = 0;
	for(int i = 1; i <= n; ++i) {
		string s = to_string(i);
		answer += s.size() % 2;
	}
	cout << answer;
}

### 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() {
	int n;
	cin >> n;
	int answer = 0;
	for(int i = 1; i <= n; ++i) {
		string s = to_string(i);
		answer += s.size() % 2;
	}
	cout << answer;
}

```