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 1.8.0) (judge verdict: Accepted)

import java.util.Scanner;

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

		// 入力値の取得
		int K = sc.nextInt();
		
		// Kが偶数なら -1 を出力して終了
		if (K % 2 == 0 || K % 5 == 0) {
			System.out.println(-1);
			sc.close();
			return;
		}
		
		int rem = 7;
		int index = 1;
		while (true) {
			if (rem % K == 0) {
				break;
			}
			rem = (rem % K) * 10 + 7;
			index++;
		}
		
		// 結果の出力
		System.out.println(index);
		
		sc.close();
	}
}