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 C (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int is753(int a) {
	int k, flg[4] = { 0, 0, 0, 1};
	while (a > 0) {
		k = a % 10;
		a /= 10;
		if (k == 3) flg[0] = 1;
		else if (k == 5) flg[1] = 1;
		else if (k == 7) flg[2] = 1;
		else {
			flg[3] = 0;
			break;
		}
	}
	return flg[0] && flg[1] && flg[2] && flg[3];
}

int log_10(int a) {
	int cnt = 0;
	while (a > 0) {
		a /= 10;
		cnt++;
	}
	return cnt;
}

int main(void) {
	int n, log_n;
	scanf("%d", &n);
	log_n = log_10(n);

	int dfs(int cur, int a) {
		int ret0, ret3, ret5, ret7;
		ret0 = (is753(a) && a <= n) ? 1 : 0;
		if (cur == log_n) {
			return ret0;
		}
		ret3 = dfs(cur + 1, 10 * a + 3);
		ret5 = dfs(cur + 1, 10 * a + 5);
		ret7 = dfs(cur + 1, 10 * a + 7);
		return ret0 + ret3 + ret5 + ret7;
	}
	
	printf("%d", dfs(0, 0));
	return 0;
}