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: Wrong Answer)

import java.util.*;

public class Main{

    final static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) {
        System.out.println(C());
    }

    public static String A() {
        int input = sc.nextInt();
        if(input >= 30){
            return "Yes";
        }
        else{
            return "No";
        }
    }

    public static int B(){
        int N = sc.nextInt();
        int D = sc.nextInt();
        int cnt = 0;

        for ( var i = 0; i< N; i++){
            int x = sc.nextInt();
            int y = sc.nextInt();
            double num = Math.sqrt(Math.pow(x,2)+Math.pow(y,2));
            if(num<=D){
                cnt++;
            }
        }
        return cnt;
    }

    public static int C(){
        int K = sc.nextInt();
        if(K%2==0){
            return -1;
        }
        else{
            int x = K%7;
            for(var i = 1; i<= K; i++){
                if(x==0){
                    return i;
                }
                else{
                    x = (x*10+7)%7;    
                }
            }
            return -1;
        }
    }
}