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);
		// 整数の入力
		int k = Integer.parseInt(sc.next());
		
    /*--------------------------------*/
    //入力
    //int k = 101;
 
      
    //数列の定義
    int i=0;
    double sum = 0;
    while(i <= k){
      sum = sum + 7 * Math.pow(10,i);
      //sum = sum + 1 * Math.pow(10,i);	//数列の定義
      //System.out.println(sum);
      // 出力
      if((int)sum%k == 0){
          System.out.println(i+1);
          break;
      }
      i++;
    }
     if(i > k){
       System.out.println("-1");
     }
 
}
}