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: Accepted)

program main
    use,intrinsic :: iso_fortran_env
    implicit none
    integer(int32):: k, n, ans
    logical,allocatable:: kishutu(:)

    read*, k
    allocate(kishutu(0:k), source = .false.)
    if (mod(k,7)==0) k=k/7
    n = mod(1,k)
    ans=1
    do while(n /= 0)
        if (kishutu(n)) then
            print'(i0)', -1
            stop
        end if
        kishutu(n) = .true.
        n = mod(n*10+1,k)
        ans=ans+1
    end do
    print'(i0)', ans
end program main