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 Go (1.14.1) (judge verdict: Accepted)

package main

import "fmt"

func main() {
	var k int
	fmt.Scan(&k)
	appears := make([]bool, k)
	count := 1
	a := 7
	a %= k
	if a == 0 {
		fmt.Println(1)
		return
	}

	for !appears[a] {
		appears[a] = true
		a = (a*10 + 7) % k
		count++
		if a == 0 {
			fmt.Println(count)
			return
		}
	}
	fmt.Println(-1)
}