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: Runtime Error)

using System;
using System.IO.Pipes;
using System.Linq;

class named
{

    static void Main()
    {
        int[] f = Console.ReadLine().Split().Select(int.Parse).ToArray();
        int fal = f[0];
        long k = 1;
        long g = 1;
int falco=0;
        if (fal % 2 == 0||fal%5==0)
        {
            Console.WriteLine("-1");

        }
        else if(fal%7==0)
        {
           falco = fal / 7;
    }
else{
falco = fal;

}
            while (true){

                if (k % falco == 0)
                {
                    Console.WriteLine(g);
                    break;

                }
                else
                {
                    k = 10^g + k;
                    g++;
                }
            


            }



        }






   




}