use std::io::{Write, Read};
fn check_(n:&i32)->bool{
    let n = *n;
    let mut logn = 1;
    let mut nums = Vec::with_capacity(4);
    while n / logn != 0{
        let a = (n % (logn * 10)) / logn;
        nums.push(a);
        logn *= 10;
    }
    if nums.len() == 1{
        return true;
    }
    let d = nums[1]  - nums[0];
    for i in 2..nums.len(){
        if nums[i - 1] + d != nums[i]{
            return false;
        }
    }
    return true;
}
fn main() {
    let mut stdin = std::io::stdin();
    let mut line = String::new();
    stdin.read_line(&mut line);
    let num = line.trim().parse::<i32>().unwrap();
    println!("{}", (1..=num).into_iter().filter(check_).count());
}

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