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 = (int) trim(fgets(STDIN));
$mods = [];

$lastMod = 7 % $K;
$mods[1] = $lastMod;

for($i = 2; $i <= $K; $i++) {
  $mod = ($lastMod * 10 + 7) % $K;
  $mods[$i] = $lastMod = $mod;
}

$n = array_search(0, $mods, true);
if($n === false) echo "-1\n";
else echo $n, "\n";