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 Julia (1.4.0) (judge verdict: Accepted)

if isfile("mystdin.txt");mystdin=open("mystdin.txt","r");redirect_stdin(mystdin);end
k=parse(Int,readline())
function main()
  ans=1
  now=mod(7,k)
  while now!=0
    ans+=1
    now=mod(7+now*10,k)
    if ans>10^6;ans=-1; break; end
  end
  println(ans)
end
main()
if isdefined(Base, :mystdin);close(mystdin);end