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 Kotlin (1.3.71) (judge verdict: Time Limit Exceeded)

import java.math.BigInteger

fun main(args: Array<String>) {
    val ks = readLine()!!
    if (ks.toInt() % 2 == 0 || ks.toInt() % 5 == 0) {
        println(-1)
        return
    }
    val k = BigInteger(ks)
    val nana = BigInteger("7")

    var seven = BigInteger("7")
    var ans = 1

    while (seven % k != BigInteger.ZERO) {
        seven = seven * BigInteger.TEN + nana
        ans++
    }


    println(ans)
}