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 {
  def main(args: Array[String]): Unit = {
    val num = scala.io.StdIn.readInt
    var check_num = Array.fill( num )( false )

    if( num%2 == 0 || num%5 == 0 ) println( -1 )
    else {
      var check = 7%num
      var count = 1
      while( check != 0 && !check_num( check ) ) {
        count += 1
        check_num( check ) = true
        check = ( check*10 + 7 )%num 
      }

      if( check%num != 0 ) println( -1 )
      else                 println( count )
    }
  }
}