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
$N = (int)trim(fgets(STDIN));
//$S = trim(fgets(STDIN));
//list($N,$D) = array_map('intval',explode(" ",trim(fgets(STDIN))));
//$A = array_map('intval',explode(" ",trim(fgets(STDIN))));


$x = 7 % $N;
$S=array();
$i=1;
while(!isset($S[$x])) {
  if ($x == 0) {
    printf("%d\n",$i);
    exit;
  }
  $S[$x]=1;
  $x = ($x*10+7)%$N;
  $i++;
}
printf("%d\n",-1);