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

class main{
    public function main(){
        fscanf(STDIN,"%d",$k);
        $a = 7%$k;
        if($k==2){
            echo "-1\n";
            return 0;
        }
        for($i=1;$i<=$k;$i++){
            if($i>1000001){
                echo "-1\n";
                return 0;
            }
            if($a===0){
                echo $i."\n";
                return 0;
            }
            $a=$a*10+7;
            $a%=$k;
        }
        echo "-1\n";
    }
}
new main();