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: Runtime Error)


import java.util.*;
class Main {

	//最大公約数・最小公倍数（セットで使う）
static int gcd (int a, int b) {return b>0?gcd(b,a%b):a;}
static int lcm (int a, int b) {return a*b/gcd(a,b);}

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);


		int n = sc.nextInt();
		int cnt = 0;
		
		
		if(n%2 == 0){
			System.out.println(-1);
			return;
		}
		
		String nana = new String();
		boolean flg = true;
		while(flg){
			cnt++;
			nana = nana + "7";
			int i = Integer.parseInt(nana);
			if(i%n == 0){
				System.out.println(cnt);
				flg = false;
				return;
			}
			
		}

		System.out.println("-1");
		}
	}