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::prelude::*;
use std::io::stdin;
use std::str::FromStr;

fn main() {
    let n: u64 = read();
    println!("{}", dfs(0, n));
}

fn dfs(s: u64, n: u64) -> u64 {
    if s > n {
        0
    } else {
        let mut ret = if is_753(s) { 1 } else { 0 };
        for x in [7, 5, 3].iter() {
            ret += dfs(s * 10 + x, n);
        }
        ret
    }
}

fn is_753(n: u64) -> bool {
    let mut n = n;
    let mut seven = 0;
    let mut five = 0;
    let mut three = 0;

    while n != 0 {
        match n % 10 {
            7 => seven += 1,
            5 => five += 1,
            3 => three += 1,
            _ => return false,
        }
        n /= 10;
    }
    seven > 0 && five > 0 && three > 0
}

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let token: String = stdin
        .lock()
        .bytes()
        .map(|b| b.unwrap() as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().unwrap()
}