https://www.acmicpc.net/problem/1065
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.print(arithmetic_sequence(sc.nextInt()));
sc.close();
}
public static int arithmetic_sequence(int num) {
int cnt = 0;
if (num < 100) {
return num;
}
else {
cnt = 99;
for (int i = 100; i <= num; i++) {
int hun = i / 100;
int ten = (i / 10) % 10;
int one = i % 10;
if ((hun - ten) == (ten - one)) {
cnt++;
}
}
}
return cnt;
}
}