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 Java (OpenJDK 11.0.6) (judge verdict: Wrong Answer)

import java.util.*;

public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        
        int k = sc.nextInt();
        int seven = 7 % k;
        int temp = -1;
        int res = seven;
        boolean divisible = false;
        int count = 1;
        List<Integer> past = new ArrayList<Integer>();

        while (!past.contains(res)) {
            past.add(res);
            temp = res;
            res = (res * 10) % k;
            res = (res + seven) % k;
            count++;
            if (res == 0) {
                divisible = true;
                break;
            }
        }

        if (divisible) {
            System.out.println(count);
        } else if (k == 1 || k == 7) {
            System.out.println(1);
        } else {
            System.out.println(-1);
        }
    }
    
    static boolean contains (int past[], int n) {
        boolean result = false;

        for (int i = 0; i < past.length; i++) {
            if (past[i] == n) {
                result = true;
                break;
            }
            if (past[i] == 0) {
                break;
            }
        }
        return result;
    }
}