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 Scala (2.13.1) (judge verdict: Accepted)

object Main extends App {
  val inputs: Seq[String] = scala.io.Source.stdin.getLines().toList
  val k = inputs.head.toInt

  println(solve(k))

  def solve(k: Int): Int = {
    val set = scala.collection.mutable.Set.empty[Int]
    var mod = 7 % k
    var count = 1

    (0 until k).foreach { i =>
      if(set.contains(mod)) {
        return -1
      }


      if(mod == 0) {
        return count
      }

      mod = (mod * 10 + 7) % k
      count = count + 1
    }

    -1
  }
}