import java.io.*
import java.util.*
import java.lang.*
import java.lang.Math.*


class LongMod(var num: Long, val MOD: Long = 1_000_000_007L) {
    init {
        if (MOD <= 0) throw Error("MOD <= 0")
        this.num = (this.num%this.MOD + this.MOD)%this.MOD
    }
    constructor(numStr: String, Base: Int=10, MOD: Long=1_000_000_007L) :
            this(0L, MOD) {
        if (numStr.isEmpty()) return
        var rv = numStr.reversed()
        var d = 1L
        rv.forEach{ c ->
            this.num += (c - '0') * d
            this.num %= MOD
            d *= Base
            d %= MOD
        }
    }
    override operator fun equals(other: Any?): Boolean {
        if (other !is LongMod) return false
        return this.num % this.MOD == other.num % this.MOD
    }
    operator fun unaryMinus(): LongMod {
        return LongMod(-this.num)
    }
    private operator fun plusAssign(other: LongMod): Unit {
        if ((this.num + other.num) >= this.MOD) {
            this.num -= this.MOD
        }
        this.num += other.num
    }
    private operator fun minusAssign(other: LongMod): Unit {
        if ((this.num + this.MOD - other.num) >= this.MOD) {
            this.num -= this.MOD
        }
        this.num += this.MOD - other.num
    }
    private operator fun timesAssign(other: LongMod): Unit {
        this.num *= other.num
        this.num %= this.MOD
    }
    operator fun plus(other: LongMod): LongMod {
        val res = LongMod(this.num, this.MOD)
        res += other
        return res
    }
    operator fun minus(other: LongMod): LongMod {
        val res = LongMod(this.num, this.MOD)
        res -= other
        return res
    }
    operator fun times(other: LongMod): LongMod {
        val res = LongMod(this.num, this.MOD)
        res *= other
        return res
    }
    fun pow(n: Long): LongMod {
        if (n == 0L) return LongMod(1L, this.MOD)
        var x = this.pow(n / 2)
        x.timesAssign(x)
        if (n % 2 == 1L) x.timesAssign(this)
        return x
    }
    fun inv(): LongMod {
        return this.pow(this.MOD - 2)
    }
    operator fun divAssign(other: LongMod): Unit {
        this *= other.inv()
    }
    operator fun div(other: LongMod): LongMod {
        val res = LongMod(this.num, this.MOD)
        res /= other
        return res
    }
}


fun solve() {
    val K = rd.readInt()
    if (K%2 == 0) {
        println(-1)
        return
    }

    var ans = -1
    var num = LongMod(7L, K.toLong())
    val Zero = LongMod(0L, K.toLong())
    val Ten = LongMod(10L, K.toLong())
    val Seven = LongMod(7L, K.toLong())
    for (n in 1..K) {
        if (num == Zero) {
            ans = n
            break
        }

        num *= Ten
        num += Seven
    }

    println(ans)
}


//val rd = debug.Reader("abc", "174", "c", "sample-1")
val rd = Reader()


fun main(args: Array<String>) {
    try {
        var exception: Throwable? = null
        val sth = Thread(null, SolveThread(), "solveThread", 128 * 1024 * 1024)
        sth.setUncaughtExceptionHandler { _, e -> exception = e }
        sth.start(); sth.join()
        if (exception != null) throw exception!!
    } catch (e: Exception) { throw e }
}
const val MOD = 1_000_000_007L; const val INF = Int.MAX_VALUE/2; const val LINF = Long.MAX_VALUE/2
const val EPS = 1e-9; fun DBLEQ(a: Double, b: Double): Boolean {return abs(a - b) < EPS}
data class IntPair(val first: Int, val second: Int)
data class To(val idx: Int, val cost: Long)
typealias ALI = ArrayList<Int>
fun <T>edge(V: Int): Array<ArrayList<T>> { return Array(V){ArrayList<T>()} }
val errPrintln: (Any) -> Unit = { msg -> System.err.println(msg) }
fun rAssert(exp: Boolean, lazyMsg: () -> String = {""}) {
    if (!exp) { val msg = lazyMsg(); errPrintln("EAssert Error: $msg"); throw Error(msg) }
}
fun tAssert(exp: Boolean, lazyMsg: () -> String = {""}) {
    if (!exp) { val msg = lazyMsg(); errPrintln("TAssert Error: $msg"); Thread.sleep(3000) }
}
class SolveThread : Runnable {
    override fun run() { solve() }
}
class Reader {
    private val br = BufferedReader(InputStreamReader(System.`in`))
    val readString: () -> String = { br.readLine() }
    val readInt: () -> Int = { br.readLine().toInt() }
    val readLong: () -> Long = { br.readLine().toLong() }
    val readIntArray: () -> IntArray = { br.readLine().split(' ').map { it.toInt() }.toIntArray() }
    val readLongArray: () -> LongArray = { br.readLine().split(' ').map { it.toLong() }.toLongArray() }
    val readListInt: () -> List<Int> = { br.readLine().split(' ').map { it.toInt() } }
    val readListLong: () -> List<Long> = { br.readLine().split(' ').map { it.toLong() } }
}


Measured memory_bytes: 51808