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: Wrong Answer)

k=gets.to_i
if k%2==0||k%5==0
  puts -1
  exit
end
#if k%7==0
#  n=k.to_s.size-1
#else
#  n=(k*7).to_s.size-1
#end
n=k
loop do
  num=("7"*n).to_i
#  print "#{n}: 余:#{num%k}"
  if num%k==0
#    puts ""
    p n
    exit
  end
#  puts " false"
  n-=1
end