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: Runtime Error)

def f(n, k):
  num_bit = 3 - bin(k).count('1')
  c = [0, 0, 1, 3]
  return 3**n - num_bit*2**n + c[num_bit]

# k = 0:(), 1:(3), 2(5), 3:(3, 5), 4:(7), 5:(3, 7), 6:(5, 7), 7:(3, 5, 7)
def solve(N, k=0):
  n = len(N)
  num_used = bin(k).count('1')
  if n==0 and num_used==3:
    return 1
  elif n==0 or n+num_used<3:
    return 0
  else:
    a = int(N[0])
    if a > 7:
      return sum([f(i, 0) for i in range(3, n+1)])
    elif a == 7:
      return f(n-1, k|2) + f(n-1, k|1) + solve(N[1:], k|4)
    elif a > 5:
      return f(n-1, k|2) + f(n-1, k|1)
    elif a == 5:
      return f(n-1, k|1) + solve(N[1:], k|2)
    elif a > 3:
      return f(n-1, k|1)
    elif a == 3:
      return solve(N[1:], k|1)
    elif a > 0:
      return 0

N = input()
base = sum([f(i, 0) for i in range(3, len(N))])
print(solve(N) + base)