Deloitte | COGNIZANT | IBM | CAPGEMINI
import java.util.Scanner;
class Solution{
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);
int n=sc.nextInt();
int count=0;
for(int i=1;i<n;i++){
int k=(int) Math.log10(i)+1;
if(k%2!=0){
count++;
}
}
System.out.println(count);
}
}
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