import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int count = 0;
        for(int i=1; i<=a; i++) {
            String b = Integer.toString(i);
            if(b.length() % 2 == 1) {
                count++;
            }
        }
        System.out.println(count);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int count = 0;
        for(int i=1; i<=a; i++) {
            String b = Integer.toString(i);
            if(b.length() % 2 == 1) {
                count++;
            }
        }
        System.out.println(count);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int count = 0;
        for(int i=1; i<=a; i++) {
            String b = Integer.toString(i);
            if(b.length() % 2 == 1) {
                count++;
            }
        }
        System.out.println(count);
    } main {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int count = 0;
        for(int i=1; i<=a; i++) {
            String b = Integer.toString(i);
            if(b.length() % 2 == 1) {
                count++;
            }
        }
        System.out.println(count);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc int count = 0; count 0 for(int i=1; i<=a; i++) {
            String b = Integer.toString(i);
            if(b.length() % 2 == 1) {
                count++;
            }
        } int i=1; int i=1; i 1 i<=a i a i++ i++ i {
            String b = Integer.toString(i);
            if(b.length() % 2 == 1) {
                count++;
            }
        } {
            String b = Integer.toString(i);
            if(b.length() % 2 == 1) {
                count++;
            }
        } String b = Integer.toString(i); b Integer.toString(i) Integer.toString Integer i if(b.length() % 2 == 1) {
                count++;
            } b.length() % 2 == 1 b.length() % 2 b.length() b.length b 2 1 {
                count++;
            } count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int count = 0;
        for(int i=1; i<=a; i++) {
            String b = Integer.toString(i);
            if(b.length() % 2 == 1) {
                count++;
            }
        }
        System.out.println(count);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int count = 0;
        for(int i=1; i<=a; i++) {
            String b = Integer.toString(i);
            if(b.length() % 2 == 1) {
                count++;
            }
        }
        System.out.println(count);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int count = 0;
        for(int i=1; i<=a; i++) {
            String b = Integer.toString(i);
            if(b.length() % 2 == 1) {
                count++;
            }
        }
        System.out.println(count);
    }
}