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 Python (3.4.3) (judge verdict: Accepted)

import itertools, operator
def combinations_with_replacement_counts(n, r):
    size = n + r - 1
    for indices in itertools.combinations(range(size), n-1):
        starts = [0] + [index+1 for index in indices]
        stops = indices + (size,)
        yield tuple(map(operator.sub, stops, starts))
        
a = (input())
ok = dict()
aller = list(range(len(a)))
out = 0
if len(a) <= 2:
	print(0)
if len(a) >= 3:
	num = int(a)
	for times in range(len(a) - 3):
		no = list(range(times + 3))
		for i in combinations_with_replacement_counts(3, times):
			for j in itertools.combinations(no, i[0] + 1):
				for k in itertools.combinations([ele for ele in no if ele not in j], i[1] +1):
					for l in itertools.combinations([ele for ele in no if ele not in j and ele not in k], i[2] + 1):
						out += 1
					
	for i in combinations_with_replacement_counts(3, len(a) - 3):
		for j in itertools.combinations(aller, i[0] + 1):
			for k in itertools.combinations([ele for ele in aller if ele not in j], i[1] +1):
				for l in itertools.combinations([ele for ele in aller if ele not in j and ele not in k], i[2] + 1):
					number = sum([3*10**ele for ele in j]) +sum([5*10**ele for ele in k]) + sum([7*10**ele for ele in l])
					if number <= num:
						out += 1
	print(out)