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: Accepted)

import java.util.Scanner;

public class Main {
	
	public static void main(String[] args)
	{
		Scanner s=new Scanner(System.in);
		
		long k=s.nextLong();
		
		long num=0;
		
		int p=0;
		int count=0;
		
		for(int i=0;i<10000000;i++)
		{
			num=((num%k)*(10%k))%k;
			num=(num%k+7%k)%k;
			
			count++;
			
			if(num==0)
			{
				p=1;
				break;
			}
		}
		
		if(p==0)
		{
			System.out.println(-1);
		}
		else
		{
			System.out.println(count);
		}
		
	}
	
}