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 {
    public static void main(String[] args) {
      Scanner sc = new Scanner(System.in);
      int ans = 0;
      int K = sc.nextInt();
      int[] A = new int[1000001];
      A[0]=7%K;
      for(int i=1; i<K; i++) {
        A[i]=(A[i-1]*10+7)%K; //ここまでで全てを終わらせる。
      } //とり合えずここで閉じて配列要素の閉じ込める。
      
      for(int i=1; i<=K; i++) {
        if(A[i]==0) {
          System.out.println(i+1);
          //break; //ループを抜ける、かつ -1 も同時に出力してしまう。
          return; //ループを抜ける、かつ戻り値を返し出力を決定する。
        } 
      }
          System.out.println(-1);
    }
  }