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
  list($k) = explode(" ", trim(fgets(STDIN)));

  if($k % 2 == 0){
    echo "-1";
    exit; 
  }

  $a = 7;
  for($i=1; $i<1000000; $i++){
    if($a % $k == 0){
      echo $i;
      exit;
    }
    $a = $a % $k;
    $a = $a * 10 + 7;
  }

  echo "-1";