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::*;
use std::str::FromStr;

pub 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")
}

// use std::cmp::{max, min};

fn main() {
  let n = read::<u64>();
  let n_str = n.to_string();
  let mut sum = 0;

  sum += dfs(String::from("3"), n_str.len(), n);
  sum += dfs(String::from("5"), n_str.len(), n);
  sum += dfs(String::from("7"), n_str.len(), n);

  println!("{}", sum);
}

fn dfs(num: String, l_keta: usize, limit: u64) -> u64 {
  let num_i = num.parse::<u64>().unwrap();

  let mut sum = 0;

  if num.contains('3') && num.contains('5') && num.contains('7') && num_i <= limit {
    sum += 1;
  }
  if num.len() > l_keta {
    return 0;
  }
  let num_3 = num.clone();
  let num_5 = num.clone();
  let num_7 = num.clone();
  sum += dfs(num_3 + "3", l_keta, limit);
  sum += dfs(num_5 + "5", l_keta, limit);
  sum += dfs(num_7 + "7", l_keta, limit);
  sum
}