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;

//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")
}

fn rec(n:usize,m:usize,buff:&mut Vec<i64>,mut ans:u32) -> u32{

    //再帰終了条件
    let mut buff_num = 0;
    for (i,b) in buff.iter().enumerate(){
        buff_num += b * 10i64.pow((buff.len()-1-i) as u32);
    }
    if (buff_num as usize) > n {
        return ans;
    }

    //753数の判定
    if buff.contains(&3) && buff.contains(&5) && buff.contains(&7){
        ans += 1;
    }

    //再帰全探索
    let v = vec![3,5,7];
    for num in v.into_iter(){
        buff.push(num);
        ans = rec(n,m,buff,ans);
        buff.pop();
    }

    ans
}
  
fn main() {
    let n: usize = read();
    let mut m = n;
    let mut keta = 0;
    while m!=0 {
        m /= 10;
        keta += 1;
    }
    let mut buff = Vec::new();
    let ans = rec(n,keta,&mut buff,0);
    print!("{}", ans);
}