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 C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;

class C
{
	static void Main(string[] args)
	{
		var input1Line = Console.ReadLine();
		var k = int.Parse(input1Line);
		var intArray = new int[k + 1];
		intArray[1] = 7 % k;
		for (int i = 2; i <= k; i++)
		{
			intArray[i] = (intArray[i - 1] * 10 + 7) % k;
		}

		for (int i = 1; i <= k; i++)
		{
			if (intArray[i] == 0)
			{
				Console.WriteLine(i);
				return;
			}
		}
		Console.WriteLine(-1);
	}
}