백준 5단계 no.3

import java.util.*;

public class Main{
    static boolean reader (int n) {
        int[] arr = new int[3];

        for (int i = 0; i < arr.length; i++) {
            arr[i] = n%10;
            n = n/10;
        }

        return (arr[0] - arr[1]) == (arr[1] - arr[2]);
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        if (n < 100) {
            System.out.print(n);
        } else if (n < 1000) {
            int count = 0;
            int m = 100;
            while(m <= n) {
                if (reader(m)) {
                    count++;
                }
                m++;
            }
            System.out.print(99+count);
        } else {
            System.out.print(144);
        }

    }
}