import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int c = 0;
        if (n < 10) {
            c = n;//1..n
        } else if (n < 100) {
            c = 9;//1...9
        } else if (n < 1_000) {
            c = n - 90;// 1..9,100..n -> n - 99 + 9
        } else if (n < 10_000) {
            c = 909;//1..9,100..999 -> 999 - 99 + 9
        } else if (n < 100_000) {
            c = n - 9090;//1..9,100..999,10000..n -> n - 9999 + 999 - 99 + 9
        } else {
            c = 90909;//1..9,100..999,10000..99999 -> 99999 - 9999 + 999 - 99 + 9
        }
        System.out.println(c);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int c = 0;
        if (n < 10) {
            c = n;//1..n
        } else if (n < 100) {
            c = 9;//1...9
        } else if (n < 1_000) {
            c = n - 90;// 1..9,100..n -> n - 99 + 9
        } else if (n < 10_000) {
            c = 909;//1..9,100..999 -> 999 - 99 + 9
        } else if (n < 100_000) {
            c = n - 9090;//1..9,100..999,10000..n -> n - 9999 + 999 - 99 + 9
        } else {
            c = 90909;//1..9,100..999,10000..99999 -> 99999 - 9999 + 999 - 99 + 9
        }
        System.out.println(c);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int c = 0;
        if (n < 10) {
            c = n;//1..n
        } else if (n < 100) {
            c = 9;//1...9
        } else if (n < 1_000) {
            c = n - 90;// 1..9,100..n -> n - 99 + 9
        } else if (n < 10_000) {
            c = 909;//1..9,100..999 -> 999 - 99 + 9
        } else if (n < 100_000) {
            c = n - 9090;//1..9,100..999,10000..n -> n - 9999 + 999 - 99 + 9
        } else {
            c = 90909;//1..9,100..999,10000..99999 -> 99999 - 9999 + 999 - 99 + 9
        }
        System.out.println(c);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int c = 0;
        if (n < 10) {
            c = n;//1..n
        } else if (n < 100) {
            c = 9;//1...9
        } else if (n < 1_000) {
            c = n - 90;// 1..9,100..n -> n - 99 + 9
        } else if (n < 10_000) {
            c = 909;//1..9,100..999 -> 999 - 99 + 9
        } else if (n < 100_000) {
            c = n - 9090;//1..9,100..999,10000..n -> n - 9999 + 999 - 99 + 9
        } else {
            c = 90909;//1..9,100..999,10000..99999 -> 99999 - 9999 + 999 - 99 + 9
        }
        System.out.println(c);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int c = 0; c 0 if (n < 10) {
            c = n;//1..n
        } else if (n < 100) {
            c = 9;//1...9
        } else if (n < 1_000) {
            c = n - 90;// 1..9,100..n -> n - 99 + 9
        } else if (n < 10_000) {
            c = 909;//1..9,100..999 -> 999 - 99 + 9
        } else if (n < 100_000) {
            c = n - 9090;//1..9,100..999,10000..n -> n - 9999 + 999 - 99 + 9
        } else {
            c = 90909;//1..9,100..999,10000..99999 -> 99999 - 9999 + 999 - 99 + 9
        } n < 10 n 10 {
            c = n;//1..n
        } c = n c n if (n < 100) {
            c = 9;//1...9
        } else if (n < 1_000) {
            c = n - 90;// 1..9,100..n -> n - 99 + 9
        } else if (n < 10_000) {
            c = 909;//1..9,100..999 -> 999 - 99 + 9
        } else if (n < 100_000) {
            c = n - 9090;//1..9,100..999,10000..n -> n - 9999 + 999 - 99 + 9
        } else {
            c = 90909;//1..9,100..999,10000..99999 -> 99999 - 9999 + 999 - 99 + 9
        } n < 100 n 100 {
            c = 9;//1...9
        } c = 9 c 9 if (n < 1_000) {
            c = n - 90;// 1..9,100..n -> n - 99 + 9
        } else if (n < 10_000) {
            c = 909;//1..9,100..999 -> 999 - 99 + 9
        } else if (n < 100_000) {
            c = n - 9090;//1..9,100..999,10000..n -> n - 9999 + 999 - 99 + 9
        } else {
            c = 90909;//1..9,100..999,10000..99999 -> 99999 - 9999 + 999 - 99 + 9
        } n < 1_000 n 1_000 {
            c = n - 90;// 1..9,100..n -> n - 99 + 9
        } c = n - 90 c n - 90 n 90 if (n < 10_000) {
            c = 909;//1..9,100..999 -> 999 - 99 + 9
        } else if (n < 100_000) {
            c = n - 9090;//1..9,100..999,10000..n -> n - 9999 + 999 - 99 + 9
        } else {
            c = 90909;//1..9,100..999,10000..99999 -> 99999 - 9999 + 999 - 99 + 9
        } n < 10_000 n 10_000 {
            c = 909;//1..9,100..999 -> 999 - 99 + 9
        } c = 909 c 909 if (n < 100_000) {
            c = n - 9090;//1..9,100..999,10000..n -> n - 9999 + 999 - 99 + 9
        } else {
            c = 90909;//1..9,100..999,10000..99999 -> 99999 - 9999 + 999 - 99 + 9
        } n < 100_000 n 100_000 {
            c = n - 9090;//1..9,100..999,10000..n -> n - 9999 + 999 - 99 + 9
        } c = n - 9090 c n - 9090 n 9090 {
            c = 90909;//1..9,100..999,10000..99999 -> 99999 - 9999 + 999 - 99 + 9
        } c = 90909 c 90909 System.out.println(c) System.out.println System.out System System.out c String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int c = 0;
        if (n < 10) {
            c = n;//1..n
        } else if (n < 100) {
            c = 9;//1...9
        } else if (n < 1_000) {
            c = n - 90;// 1..9,100..n -> n - 99 + 9
        } else if (n < 10_000) {
            c = 909;//1..9,100..999 -> 999 - 99 + 9
        } else if (n < 100_000) {
            c = n - 9090;//1..9,100..999,10000..n -> n - 9999 + 999 - 99 + 9
        } else {
            c = 90909;//1..9,100..999,10000..99999 -> 99999 - 9999 + 999 - 99 + 9
        }
        System.out.println(c);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int c = 0;
        if (n < 10) {
            c = n;//1..n
        } else if (n < 100) {
            c = 9;//1...9
        } else if (n < 1_000) {
            c = n - 90;// 1..9,100..n -> n - 99 + 9
        } else if (n < 10_000) {
            c = 909;//1..9,100..999 -> 999 - 99 + 9
        } else if (n < 100_000) {
            c = n - 9090;//1..9,100..999,10000..n -> n - 9999 + 999 - 99 + 9
        } else {
            c = 90909;//1..9,100..999,10000..99999 -> 99999 - 9999 + 999 - 99 + 9
        }
        System.out.println(c);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int c = 0;
        if (n < 10) {
            c = n;//1..n
        } else if (n < 100) {
            c = 9;//1...9
        } else if (n < 1_000) {
            c = n - 90;// 1..9,100..n -> n - 99 + 9
        } else if (n < 10_000) {
            c = 909;//1..9,100..999 -> 999 - 99 + 9
        } else if (n < 100_000) {
            c = n - 9090;//1..9,100..999,10000..n -> n - 9999 + 999 - 99 + 9
        } else {
            c = 90909;//1..9,100..999,10000..99999 -> 99999 - 9999 + 999 - 99 + 9
        }
        System.out.println(c);
    }
}
