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++ (GCC 9.2.1) (judge verdict: Wrong Answer)

#include<iostream>
#include<cmath>
using namespace std;
int main()
{
	int K;
	int c = 0;
	int An= 1;
	int n = 1;
	int Bn = 0;
	int m = 1;
	cin >> K;
	for (;;)
	{
		if (n == 1)
		{

		}
		else
		{
			An = An + pow(10, m);
			m = m + 1;
		}

		Bn = 7 * An;
		
		if (Bn>= pow(10,6))
		{
			cout << -1;
			break;
		}


		if (Bn % K == 0)
		{
			cout << n;
			break;
		}
		++n;
	}
}