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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;

public class Main {
	public static void main (String[] args) throws IOException{
	    InputStreamReader reader = new InputStreamReader(System.in, StandardCharsets.UTF_8);
	    BufferedReader in = new BufferedReader(reader);
		int n = Integer.parseInt(in.readLine());
		int cnt = 0;
		long num = 7;

		if(n % 2 == 0) {
			System.out.println(-1);
			return;
		}
		for(int i=0; i < 100; i++) {
			cnt++;
			if(i == 0) {
				if(num % n == 0) {
					System.out.println(cnt);
					break;
				}
				continue;
			}
			else{
				num += 7*(long)Math.pow(10, i);
				if(num % n == 0) {
					System.out.println(cnt);
					break;
				}
			}
		}


	}
}