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


class PriQueMax<T>() :
        PriorityQueue<T>(Collections.reverseOrder()) {}

fun solve() {
    val N = rd.readInt()
    val A = rd.readLongArray()
    val B = rd.readLongArray()

    if (A.sum() < B.sum()) {
        println(-1)
        return
    }

    var ok = true
    for (i in 0 until N) {
        if (A[i] < B[i]) {
            ok = false
            break
        }
    }
    if (ok) {
        println(0)
        return
    }

    val diff = ArrayList<Long>()
    val pq = PriQueMax<Long>()
    for (i in 0 until N) {
        if (A[i] < B[i]) diff.add(B[i] - A[i])
        else if (A[i] > B[i]) pq.add(A[i] - B[i])
    }

    var cnt = diff.size
    var sum = diff.sum()

    while (sum > 0) {
        val hi = if (pq.isNotEmpty()) pq.poll()!! else -1
        if (hi < 0) {
            println(-1)
            return
        }
        sum -= hi
        cnt++
    }

    val ans = cnt
    println(ans)
}


//val rd = debug.Reader("etc", "keyence2019", "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 }
    finally { rd.close() }
}
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() } }
    val readListIntCol: (Int) -> List<Int> = { N -> (0 until N).map { readInt() } }
    val readListLongCol: (Int) -> List<Long> = { N -> (0 until N).map { readLong() } }
    val close: () -> Unit = { br.close() }
    protected fun finalize() { close() }
}


Measured memory_bytes: 61132