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 <math.h>

int main(void) {

  long n;
  scanf("%ld", &n);
  long answer = 0;
  int generate[9];
  long number;
  int has7,has5,has3;
  for (int digits = 3; digits <= 9; digits++) {
    if (pow(10,digits-1) > n) {
      break;
    }
    for (int i = 0; i < digits; i++) {
      generate[i] = 0;
    }
    for (int i = 0; i < pow(3,digits)-1; i++) {
      number = 0;
      has3 = 0;
      has5 = 0;
      has7 = 0;
      for (int j = 0; j < digits; j++) {
        if (generate[j] == 0) {
          has3 = 1;
          number += 3*pow(10,j);
        }
        if (generate[j] == 1) {
          has5 = 1;
          number += 5*pow(10,j);
        }
        if (generate[j] == 2) {
          has7 = 1;
          number += 7*pow(10,j);
        }
      }
      if (has3 == 1 && has5 == 1 && has7 == 1 && number <= n) {
        answer++;
      }
      generate[0]++;
      for (int j = 1; j < digits; j++) {
        generate[j] += generate[j-1]/3;
        generate[j-1] %= 3;
      }
    }
  }
  printf("%ld\n", answer);

  return 0;
}