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: Accepted)

private fun getInts(): IntArray {
    return readLine()!!.split(" ").map {it.toInt()}.toIntArray()
}

fun main(){
    val k = getInts()[0]
    val flags = Array(1000000) {i->false}
    var count = 1
    var r = 7

    if (k %2 == 0 || k %5 == 0) {
        print(-1)
        return
    }

    while(true){
        // 割ってみる。
        val quot = r % k
        // もうやった。ループしているから失敗。
        if (flags[quot]) {
            print(-1)
            return
        }
        if (quot == 0) {
            // うまく行った。この値。
            print(count)
            return
        } else {
            // この値はだめだった。カウンタを回し、更新して次へ。
            count++
            flags[quot] = true
            r = quot*10 + 7
        }
    }
}