import java.util.*;
public class Main {
		
	public static void main(String[] args) {		
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		sc.close();
		
		int count = 0;
		for(int i=1;i<=N;i++) {
			
			//111 -> 11 -> 1 -> 0
			int cnt = 0;
			
			int tmp = i;
			
			while(tmp != 0) {
				tmp/=10; // i = i / 10 ;  i = i + 3 -> i+=3; i = i+1 -> i++
				cnt ++;
			}
			
			if(cnt % 2 == 1) count ++;
			
		}
		System.out.println(count);
	}
	
} import java.util.*; util.* java public class Main {
		
	public static void main(String[] args) {		
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		sc.close();
		
		int count = 0;
		for(int i=1;i<=N;i++) {
			
			//111 -> 11 -> 1 -> 0
			int cnt = 0;
			
			int tmp = i;
			
			while(tmp != 0) {
				tmp/=10; // i = i / 10 ;  i = i + 3 -> i+=3; i = i+1 -> i++
				cnt ++;
			}
			
			if(cnt % 2 == 1) count ++;
			
		}
		System.out.println(count);
	}
	
} Main public static void main(String[] args) {		
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		sc.close();
		
		int count = 0;
		for(int i=1;i<=N;i++) {
			
			//111 -> 11 -> 1 -> 0
			int cnt = 0;
			
			int tmp = i;
			
			while(tmp != 0) {
				tmp/=10; // i = i / 10 ;  i = i + 3 -> i+=3; i = i+1 -> i++
				cnt ++;
			}
			
			if(cnt % 2 == 1) count ++;
			
		}
		System.out.println(count);
	} main {		
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		sc.close();
		
		int count = 0;
		for(int i=1;i<=N;i++) {
			
			//111 -> 11 -> 1 -> 0
			int cnt = 0;
			
			int tmp = i;
			
			while(tmp != 0) {
				tmp/=10; // i = i / 10 ;  i = i + 3 -> i+=3; i = i+1 -> i++
				cnt ++;
			}
			
			if(cnt % 2 == 1) count ++;
			
		}
		System.out.println(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc sc.close() sc.close sc int count = 0; count 0 for(int i=1;i<=N;i++) {
			
			//111 -> 11 -> 1 -> 0
			int cnt = 0;
			
			int tmp = i;
			
			while(tmp != 0) {
				tmp/=10; // i = i / 10 ;  i = i + 3 -> i+=3; i = i+1 -> i++
				cnt ++;
			}
			
			if(cnt % 2 == 1) count ++;
			
		} int i=1; int i=1; i 1 i<=N i N i++ i++ i {
			
			//111 -> 11 -> 1 -> 0
			int cnt = 0;
			
			int tmp = i;
			
			while(tmp != 0) {
				tmp/=10; // i = i / 10 ;  i = i + 3 -> i+=3; i = i+1 -> i++
				cnt ++;
			}
			
			if(cnt % 2 == 1) count ++;
			
		} {
			
			//111 -> 11 -> 1 -> 0
			int cnt = 0;
			
			int tmp = i;
			
			while(tmp != 0) {
				tmp/=10; // i = i / 10 ;  i = i + 3 -> i+=3; i = i+1 -> i++
				cnt ++;
			}
			
			if(cnt % 2 == 1) count ++;
			
		} int cnt = 0; cnt 0 int tmp = i; tmp i while(tmp != 0) {
				tmp/=10; // i = i / 10 ;  i = i + 3 -> i+=3; i = i+1 -> i++
				cnt ++;
			} tmp != 0 tmp 0 {
				tmp/=10; // i = i / 10 ;  i = i + 3 -> i+=3; i = i+1 -> i++
				cnt ++;
			} tmp/=10 tmp 10 cnt ++ cnt if(cnt % 2 == 1) count ++; cnt % 2 == 1 cnt % 2 cnt 2 1 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 N = sc.nextInt();
		sc.close();
		
		int count = 0;
		for(int i=1;i<=N;i++) {
			
			//111 -> 11 -> 1 -> 0
			int cnt = 0;
			
			int tmp = i;
			
			while(tmp != 0) {
				tmp/=10; // i = i / 10 ;  i = i + 3 -> i+=3; i = i+1 -> i++
				cnt ++;
			}
			
			if(cnt % 2 == 1) count ++;
			
		}
		System.out.println(count);
	}
	
} public class Main {
		
	public static void main(String[] args) {		
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		sc.close();
		
		int count = 0;
		for(int i=1;i<=N;i++) {
			
			//111 -> 11 -> 1 -> 0
			int cnt = 0;
			
			int tmp = i;
			
			while(tmp != 0) {
				tmp/=10; // i = i / 10 ;  i = i + 3 -> i+=3; i = i+1 -> i++
				cnt ++;
			}
			
			if(cnt % 2 == 1) count ++;
			
		}
		System.out.println(count);
	}
	
} Main
import java.util.*;
public class Main {
		
	public static void main(String[] args) {		
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		sc.close();
		
		int count = 0;
		for(int i=1;i<=N;i++) {
			
			//111 -> 11 -> 1 -> 0
			int cnt = 0;
			
			int tmp = i;
			
			while(tmp != 0) {
				tmp/=10; // i = i / 10 ;  i = i + 3 -> i+=3; i = i+1 -> i++
				cnt ++;
			}
			
			if(cnt % 2 == 1) count ++;
			
		}
		System.out.println(count);
	}
	
}