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 Fortran (GNU Fortran 9.2.1) (judge verdict: Wrong Answer)

program answer
  implicit none
  integer(8) :: i, K, a
  read(*,*) k

  if(k==1) then
     write(*,*) '1'
     stop
  else if(k==3) then
     write(*,*) '3'
     stop
  else if(mod(k,5)==0) then
     write(*,*) '-1'
     stop
  else if(k==7) then
     write(*,*) '1'
     stop
  else if(mod(k,2)==0) then
     write(*,*) '-1'
     stop
  end if
 do i = 1, 12
     if(mod(7*(10**i-1)/9,K)==0) then
        write(*,*) i
        stop
     end if
  end do

  a=0
  do i = 3, int(sqrt(dble(K)))+1, 2
     if(mod(K,i)==0) then
	a=i
        exit
     end if
  end do

  if(a==0) then
     write(*,*) k-1
     stop
  end if
 stop
 end program answer