#include <iostream>
#include <string>
using namespace std;

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

int main() {
	int N, ans = 0;
	cin >> N;
	for (int i = 1; i <= N; ++i) {
		if (to_string(i).size() % 2) ++ans;
	}
	cout << ans;
}
```