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: Wrong Answer)

fun main() {
    val k = readLine()?.toInt() ?: return
    if (k % 2 == 0 || k == 5) {
        println("-1")
        return
    }
    val kk = if (k % 7 == 0) k / 7 else k
    if (kk == 1) {
        println("1")
        return
    }
    var r = 10L
    1.until(kk).forEach {
        r %= kk
        if (r == 1L) {
            println(it.toString())
            return
        }
        r *= 10
    }
}