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: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ABC174
{
    class Program
    {
        static void Main(string[] args)
        {
            int K;
            K = int.Parse(Console.ReadLine());
            //標準入力Kを受け取る
            int ans = -1;
            int num = 7;
            for (int i = 0; i < 7; i++)
            {
                double n = 0;
                for(int j = 0; j <= i; j++)
                {
                    n += num * Math.Pow(10, j);
                }
                
                if (n % K == 0)
                {
                    ans = i;
                    break;
                }
            }
            Console.WriteLine(ans);
        }
    }
}