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: Accepted)

import java.util.*;
import java.io.*;
public class Main extends PrintWriter {
    Main()
    {
        super(System.out);
    }
    public static void main(String args[]) {
      Main o=new Main();
      o.main();
      o.flush();
      o.close();
    }
    void main()
    {
        Scanner sc=new Scanner(System.in);
        int mod=sc.nextInt();
        int val=7%mod;
            int i;
            for(i=1;i<=mod;i++)
            {
                if(val==0)
                {
                    println(i);
                    return ;
                }
                val=((val*10)+7)%mod;
            }
            println(-1);
            
        
        sc.close();
    }
}