#pragma warning disable

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.Serialization.Formatters.Binary;
using System.Text;
using System.Text.RegularExpressions;
using System.Diagnostics;
using System.Numerics;
using System.Collections;

static class MainClass
{
    public static void Main(string[] args)
    {

        var N = Console.ReadLine().ToInt32();

        var An = Console.ReadLine().SplittedStringToInt64List();
        var Bn = Console.ReadLine().SplittedStringToInt64List();
        var newlist = new long[N];
        for (int i = 0; i < N; i++)
        {
            newlist[i] = An[i] - Bn[i];
        }

        var sumA = An.Sum();
        var sumB = Bn.Sum();

        if (sumA < sumB)
        {
            Console.WriteLine(-1);
        }
        else
        {
            var count = 0;
            var items = new Queue<long>(newlist.OrderBy(x => x).ToList());
            var before = 0l;
            var afterqueue = new Queue<long>(newlist.OrderByDescending(x => x).ToList());
            while (true)
            {
                var ii = items.Dequeue();
                
                if (ii >= 0)
                    break;
                count++;

                while (true)
                {

                    if (before == 0)
                    {
                        before = afterqueue.Dequeue();
                        count++;

                    }
                    if (ii == 0)
                        break;
                    if (before >= -ii)
                    {
                        before += ii;
                        ii = 0;

                    }
                    else
                    {
                        ii += before;
                        before = 0;
                    }
                }
                
                
            }
            Console.WriteLine(count);
        }

        Console.ReadLine();
    }

    

    #region ライブラリ
    public static long ToInt64(this string str) => long.Parse(str);
    public static int ToInt32(this string str) => int.Parse(str);
    public static BigInteger ToBigInteger(this string str) => BigInteger.Parse(str);
    public static List<string> SplittedStringToList(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).ToList();
    public static List<int> SplittedStringToInt32List(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => int.Parse(x)).ToList();
    public static List<long> SplittedStringToInt64List(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => long.Parse(x)).ToList();
    public static List<BigInteger> SplittedStringToBigInteger(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => BigInteger.Parse(x)).ToList();
    public const int INF = int.MaxValue / 2;
    public const long LONGINF = long.MaxValue / 2;

    public static int Max(params int[] values)
    {
        var maxes = -1;
        for (int i = 0; i < values.Length; i++)
        {
            maxes = Math.Max(values[i], maxes);
        }
        return maxes;
    }

    public static void PrintArray(int[,] array)
    {
        for (int i = 0; i < array.GetLength(0); i++)
        {
            var sb = new StringBuilder();
            for (int j = 0; j < array.GetLength(1); j++)
            {
                sb.Append(array[i, j]).Append(" ");
            }
            Console.WriteLine(sb.ToString());
        }
    }
    // public static int[]

    #endregion
}



Measured memory_bytes: 34616