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 (1.42.0) (judge verdict: Accepted)

use proconio::input;

struct Helper {
  pub count: usize,
  pub n: usize
}

impl Helper {
  fn traverse(&mut self, i: usize, v: usize) {
    if i == 10 {
      if v <= self.n && self.is_safe(v) {
        self.count += 1;
      }
      return
    }
      
    self.traverse(i+1, v+ 10usize.pow(i as u32)*7);
    self.traverse(i+1, v+ 10usize.pow(i as u32)*5);
    self.traverse(i+1, v+ 10usize.pow(i as u32)*3);

    if v <= self.n && self.is_safe(v) {
      self.count += 1;
    }
  }
  
  fn is_safe(&self, mut val: usize) -> bool {
    let mut f3 = false;
    let mut f5 = false;
    let mut f7 = false;
    
    while 0 < val {
      let v = val % 10;
      if v == 3 {
        f3 = true;
      } else if v == 5 {
        f5 = true;
      } else if v == 7 {
        f7 = true;
      } else {
        f3 = false;
        break
      }
      val /= 10;
    }
    
    f3 && f5 && f7
  }
}

fn main() {
  input! {
    n: usize,
  }

  let mut helper = Helper { count: 0, n };
  helper.traverse(0, 0);
  
 
  println!("{}", helper.count);
}