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: Wrong Answer)

<?php

$k = trim(fgets(STDIN));

$arr = [7, 77, 777, 7777, 77777, 777777, 7777777, 77777777];

$count = 1;

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

foreach ($arr as $num) {
    if ($num % $k != 0) {
        $count++;
    } else {
        echo $count;
        exit;
    }
}