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.Scanner;

public class Main{
	public static void main(String [] args) {
		Scanner sc = new Scanner(System.in);
		int K = sc.nextInt();
		float A = 7;
		int a = 0;
		int k = String.valueOf( K ).length();
		
		if((K % 2) == 0) {
			System.out.println(-1);
		}else {
			for (int f = 1; f < k;  f++) {
				A = (A * 10) + 7; 
			}
			for(int i = k;  i < (k * 10); i++) {
				if((A%K) == 0) {
					a = i;
					i = i + 1000000;
				}
				else						A = (A * 10) + 7; 
				//System.out.println(A);
				//System.out.println(A / K + "/n");
			}
			
			if(0 < a)						System.out.println(a);
			else								System.out.println(-1);
		}
	}
}