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 K = sc.nextInt();
	if (K%2 == 0) System.out.print(-1);
	else {
	    for (long i=1; i<=K*K*7; i++) {
		String num = Long.toString(K*i);
		boolean isTrue = false;
		for (int j=0; j<num.length(); j++) {
		    if (num.charAt(j) != '7') { break; }
		    if (j == num.length()-1) isTrue = true;
		}
		if (isTrue) { System.out.print(num.length()); break; }
	    }
	}
    }
}