Problem:
Score : 300 points

Problem Statement

You are given an integer N. Among the integers between 1 and N (inclusive), how many Shichi-Go-San numbers (literally "Seven-Five-Three numbers") are there?

Here, a Shichi-Go-San number is a positive integer that satisfies the following condition:

When the number is written in base ten, each of the digits 7, 5 and 3 appears at least once, and the other digits never appear.

Constraints

1 \leq N < 10^9

N is an integer.

Input

Input is given from Standard Input in the following format:

N

Output

Print the number of the Shichi-Go-San numbers between 1 and N (inclusive).

Sample Input 1

575

Sample Output 1

4

There are four Shichi-Go-San numbers not greater than 575: 357, 375, 537 and 573.

Sample Input 2

3600

Sample Output 2

13

There are 13 Shichi-Go-San numbers not greater than 3600: the above four numbers, 735, 753, 3357, 3375, 3537, 3557, 3573, 3575 and 3577.

Sample Input 3

999999999

Sample Output 3

26484

Solution in Rust (1.15.1) (judge verdict: Time Limit Exceeded)

const CHARS_753: [char; 3] = ['7', '5', '3'];

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn count(s: &String, c: char) -> i32 {
    let chars_vec: Vec<char> = s.chars().collect();
    chars_vec.iter().filter(|cmp_c| **cmp_c == c).count() as i32
}

fn dfs(s: String, n: i32) -> i32 {
    if s.parse::<i32>().unwrap_or(0) > n {
        0
    }
    else {
        let is_753   = CHARS_753.iter().all(|c| count(&s, *c) > 0);
        let sum: i32 = CHARS_753.iter().map(|c| {
            let mut new_string = s.clone();
            new_string.push(*c);
            dfs(new_string, n)
        }).sum();
        sum + if is_753 { 1 } else { 0 }
    }
}

fn main() {
    let n: i32 = read();
    println!("{}", dfs("".to_string(), n));
}