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 n=sc.nextInt();
		if(n<7) System.out.println("-1");
		else
		{
			long seven=7;
			int dig=(int)Math.log10(n)+1;
			int digc=dig;
			while(dig>1)
			{
				dig--;
				seven+=Math.pow(10, dig)*7;	
			}
			//System.out.println(seven);
			long count=digc;
			while(seven%n!=0)
			{
				count++;
				
				seven+=Math.pow(10, digc)*7;
				digc++;
			//	System.out.println(seven);
				
//				try
//				{
//				    Thread.sleep(1000);
//				}
//				catch(InterruptedException ex)
//				{
//				    Thread.currentThread().interrupt();
//				}
			}
			System.out.println(count);
		}
}
}