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.lang.*;

public class Main{
    public static void main(String[]args){
	Scanner sc = new Scanner(System.in);
    int K= sc.nextInt();
    int L=0;
    int ans=-1;
    if(K%7==0){
        L=9*K/7;
    }else{
        L=9*K;
    }

    int R=1;
    for(int i=1; i<L; i++){
        R =(R*10)%L;
        if(R==1){
            ans =i;
            break;
        }
      }
    System.out.println(ans);
    }
}