Problem:
Score : 300 points

Problem Statement

Takahashi loves the number 7 and multiples of K.

Where is the first occurrence of a multiple of K in the sequence 7,77,777,\ldots? (Also see Output and Sample Input/Output below.)

If the sequence contains no multiples of K, print -1 instead.

Constraints

1 \leq K \leq 10^6

K is an integer.

Input

Input is given from Standard Input in the following format:

K

Output

Print an integer representing the position of the first occurrence of a multiple of K. (For example, if the first occurrence is the fourth element of the sequence, print 4.)

Sample Input 1

101

Sample Output 1

4

None of 7, 77, and 777 is a multiple of 101, but 7777 is.

Sample Input 2

2

Sample Output 2

-1

All elements in the sequence are odd numbers; there are no multiples of 2.

Sample Input 3

999983

Sample Output 3

999982

Solution in Ruby (2.7.1) (judge verdict: Accepted)

K = gets.to_i
７ = [
	[],
	[7,6,5,4,3,2,1,0,9,8],
	[],
	[9,2,5,8,1,4,7,0,3,6],
	[],
	[],
	[],
	[1,8,5,2,9,6,3,0,7,4],
	[],
	[3,4,5,6,7,8,9,0,1,2]
][K%10].map!{|_|_*K}
if ７.empty?
	p(-1)
	exit
end

n = 0
k = ７[0]
while 0<k
	n += 1
	k += ７[k%10]
	k /= 10
end
p n