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: Accepted)

import java.util.*;
import java.math.RoundingMode;
import java.math.BigDecimal;
 
 
 
public class Main{
	public static void main (String[] args){
		Scanner sc = new Scanner(System.in);
		long k = sc.nextLong();
		long seven = 7;
		long count = 0;
		long mod = 0;
		boolean able = false;
		for(int i = 0; i < k; i++) {
			mod=(mod*10+7)%k;
			count++;
			if(mod == 0) {
				able = true;
				break;
			}
		}
		System.out.println(able? count : -1);
    }
}