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

[$N ] = fscanf(STDIN, "%d");
$a = 7;
$count = 1;
while($a < intdiv(PHP_INT_MAX , 11)){
    if($a% $N===0){
        echo $count;
        exit;
    }
    $a *= 10;
    $a += 7;
    $count++;
}
if($N % 7 === 0){
    $N /= 7;
}
if(gmp_prob_prime($N)){
    if($N != 2 && $N != 5 && $N != 3){
        echo $N-1;
        exit;
    }
}
echo -1;