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: Accepted)

use std::io::{stdin, Read};
use std::str::FromStr;

// https://qiita.com/tubo28/items/e6076e9040da57368845
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

#[allow(dead_code)]
fn main() {
    let n = read::<String>()
        .chars()
        .map(|c| c.to_digit(10).unwrap())
        .collect::<Vec<_>>();

    let mut q = vec![vec![]];
    let mut ans = 0;
    let c753 = vec![7, 5, 3];

    use std::collections::HashSet;
    while let Some(v) = q.pop() {
        for &c in &c753 {
            let mut vv = v.clone();
            vv.push(c);
            if is_smaller(&vv, &n) {
                let mut s = HashSet::new();
                s.insert(3);
                s.insert(5);
                s.insert(7);
                for i in 0..vv.len() {
                    s.remove(&vv[i]);
                }
                if s.is_empty() {
                    ans += 1;
                }
                q.push(vv)
            }
        }
    }
    println!("{}", ans);

    fn is_smaller(vv: &Vec<u32>, n: &Vec<u32>) -> bool {
        if vv.len() < n.len() {
            true
        } else if vv.len() == n.len() {
            for i in 0..n.len() {
                if vv[i] < n[i] {
                    return true;
                } else if vv[i] == n[i] {
                    // pass
                } else {
                    return false;
                }
            }
            true
        } else {
            false
        }
    }
}