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 scan = new Scanner(System.in);
		int k = scan.nextInt();
		int c_k = k;
		int seven = 0;
		int ans = 0;

		c_k %= 10;

		if(k % 2 == 0 ) {
			System.out.println(-1);

		}else {
			if(c_k == 1 || c_k == 3 || c_k == 7) {
				for(int i = 1;;i++) {
					seven = (seven * 10) + 7;

					if(seven % k == 0) {
						ans = i;
						break;
					}
				}
				System.out.println(ans);
			}else {
				System.out.println(-1);
			}
		}
	}
}