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 Perl (5.26.1) (judge verdict: Wrong Answer)

my $k=<>; chomp $k;my $length=length$k;
my $seven='7' x $length;
my $p=(7*(10**$length))%$k;
my $mod=$seven%$k;
if($k=~/1$/ or $k=~/3$/ or $k=~/7$/ or $k=~/9$/){while(1){if($mod==0){last;};
$mod=($mod+$p)%$k;$p=($p*10)%$k; $length++;last;}print $length;} else {print "-1";}