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: Time Limit Exceeded)

import java.util.*;
public class Main{
	public static void main(String[] args){
        Scanner s=new Scanner(System.in);
        int k=s.nextInt();
        if(k%2==0){
            System.out.println(-1);
            return;
        }
        int temp=k;
        int count=0;
        while(temp!=0){
            temp=temp/10;
            count++;
        }

        StringBuilder sb=new StringBuilder();
        for(int i=0;i<count;i++)
            sb.append('7');

        long num=Integer.parseInt(sb.toString());
        
        int res=1;
        while(num%k!=0){
            long rem=num%k;
            res++;
            num=rem*10+7;
        }
        System.out.println(res+count-1);
    }
}