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 PHP (7.4.4) (judge verdict: Accepted)

<?php
$k=trim(fgets(STDIN));
if($k%2==0 or $k%5==0){
  echo -1;
  exit;
}
$m=7;
$i=1;
while(1){
  $m%=$k;
  if($m==0){
    echo $i;
    exit;
  }elseif(isset($r[$m])){
    echo -1;
    exit;
  }else{
    $r[$m]=1;
  }
  ++$i;
  $m=$m*10+7;
}