import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
    	Scanner s = new Scanner(System.in);
      	int inputNumber = s.nextInt();
      	int digits = String.valueOf(inputNumber).length();
      	int ans = 0;
      	int size = inputNumber;

		int cnt = 0;
      	for (int i = 0; i < size; i++) {
        	if (String.valueOf(inputNumber).length() % 2 == 1) {
            	ans++;
            }
          inputNumber--;
        }
      
		System.out.println(ans);
    }
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
    	Scanner s = new Scanner(System.in);
      	int inputNumber = s.nextInt();
      	int digits = String.valueOf(inputNumber).length();
      	int ans = 0;
      	int size = inputNumber;

		int cnt = 0;
      	for (int i = 0; i < size; i++) {
        	if (String.valueOf(inputNumber).length() % 2 == 1) {
            	ans++;
            }
          inputNumber--;
        }
      
		System.out.println(ans);
    }
} Main public static void main(String[] args) {
    	Scanner s = new Scanner(System.in);
      	int inputNumber = s.nextInt();
      	int digits = String.valueOf(inputNumber).length();
      	int ans = 0;
      	int size = inputNumber;

		int cnt = 0;
      	for (int i = 0; i < size; i++) {
        	if (String.valueOf(inputNumber).length() % 2 == 1) {
            	ans++;
            }
          inputNumber--;
        }
      
		System.out.println(ans);
    } main {
    	Scanner s = new Scanner(System.in);
      	int inputNumber = s.nextInt();
      	int digits = String.valueOf(inputNumber).length();
      	int ans = 0;
      	int size = inputNumber;

		int cnt = 0;
      	for (int i = 0; i < size; i++) {
        	if (String.valueOf(inputNumber).length() % 2 == 1) {
            	ans++;
            }
          inputNumber--;
        }
      
		System.out.println(ans);
    } Scanner s = new Scanner(System.in); s new Scanner(System.in) int inputNumber = s.nextInt(); inputNumber s.nextInt() s.nextInt s int digits = String.valueOf(inputNumber).length(); digits String.valueOf(inputNumber).length() String.valueOf(inputNumber).length String.valueOf(inputNumber) String.valueOf String inputNumber int ans = 0; ans 0 int size = inputNumber; size inputNumber int cnt = 0; cnt 0 for (int i = 0; i < size; i++) {
        	if (String.valueOf(inputNumber).length() % 2 == 1) {
            	ans++;
            }
          inputNumber--;
        } int i = 0; int i = 0; i 0 i < size i size i++ i++ i {
        	if (String.valueOf(inputNumber).length() % 2 == 1) {
            	ans++;
            }
          inputNumber--;
        } {
        	if (String.valueOf(inputNumber).length() % 2 == 1) {
            	ans++;
            }
          inputNumber--;
        } if (String.valueOf(inputNumber).length() % 2 == 1) {
            	ans++;
            } String.valueOf(inputNumber).length() % 2 == 1 String.valueOf(inputNumber).length() % 2 String.valueOf(inputNumber).length() String.valueOf(inputNumber).length String.valueOf(inputNumber) String.valueOf String inputNumber 2 1 {
            	ans++;
            } ans++ ans inputNumber-- inputNumber System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
	public static void main(String[] args) {
    	Scanner s = new Scanner(System.in);
      	int inputNumber = s.nextInt();
      	int digits = String.valueOf(inputNumber).length();
      	int ans = 0;
      	int size = inputNumber;

		int cnt = 0;
      	for (int i = 0; i < size; i++) {
        	if (String.valueOf(inputNumber).length() % 2 == 1) {
            	ans++;
            }
          inputNumber--;
        }
      
		System.out.println(ans);
    }
} public class Main {
	public static void main(String[] args) {
    	Scanner s = new Scanner(System.in);
      	int inputNumber = s.nextInt();
      	int digits = String.valueOf(inputNumber).length();
      	int ans = 0;
      	int size = inputNumber;

		int cnt = 0;
      	for (int i = 0; i < size; i++) {
        	if (String.valueOf(inputNumber).length() % 2 == 1) {
            	ans++;
            }
          inputNumber--;
        }
      
		System.out.println(ans);
    }
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
    	Scanner s = new Scanner(System.in);
      	int inputNumber = s.nextInt();
      	int digits = String.valueOf(inputNumber).length();
      	int ans = 0;
      	int size = inputNumber;

		int cnt = 0;
      	for (int i = 0; i < size; i++) {
        	if (String.valueOf(inputNumber).length() % 2 == 1) {
            	ans++;
            }
          inputNumber--;
        }
      
		System.out.println(ans);
    }
}