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 baisuu_search
    integer(8) :: K, i
    integer(8) :: c = 0
    logical :: f = .false.

    read *, K
    do i = 7 ,2**20-1, i*10+1
        c = c + 1
        if(mod(i, K) .eq. 0)then
            f = .true.
        end if
        if(f .eqv. .true.)exit
    end do
    if(f .eqv. .true.)then
        print *, c
    else
        print *, '-1'
    end if
end program