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: Output Limit Exceeded)

<?php

$k = fgets(STDIN);
$s = 7;
$flag = true;
$result=1;

while($flag){
    if($k%2==0){
        echo "-1\n";
    }
    if($s%$k==0){
        $flag=false;
    }else{
        $result++;
        $s=$s*10+7;
        if($s>php_int_max){
            while($s>php_int_max){
                $s-$k;
            }
        }
    }
}

echo $result."\n";
// echo $s."\n";
// echo $s/$k."\n";