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.io.FileNotFoundException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) throws FileNotFoundException {

//    	File file = new File("src/in.txt");

        //コード
//    	Scanner sc = new Scanner(file);
    	Scanner sc = new Scanner(System.in);
    	int K = sc.nextInt();
    	if(K%2==0||K%5==0) {
    		System.out.println(-1);
    	} else {
//    		BigInteger a = BigInteger.valueOf(K);
//    		BigInteger b = BigInteger.valueOf(K);
//    		boolean flg = true;
//    		String S = "";
//    		while(flg==true) {
//    			a =a.add(b);
//    			S = a.toString();
//    			if(S.matches("7*")) {
//    				flg = false;
//    			}
//    		}
    		int a = 0;
    		boolean flg = true;
    		int count = 0;
    		while(flg) {
    			a = (a*10+7)%K;
    			count++;
    			if(a==0) {
    				flg=false;
    			}

    		}

    		System.out.println(count);
    	}
    }

}