using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
//using System.Text;
//using System.Text.RegularExpressions;
//using System.Globalization;
//using System.Diagnostics;
using static System.Console;
//using System.Numerics;
//using static System.Math;
//using pair = Pair<int, int>;

class Program
{
    static void Main()
    {
        //SetOut(new StreamWriter(OpenStandardOutput()) { AutoFlush = false });
        new Program().solve();
        Out.Flush();
    }
    readonly Scanner cin = new Scanner();
    readonly int[] dd = { 0, 1, 0, -1, 0 }; //→↓←↑
    readonly int mod = 1000000007;
    void chmax<T>(ref T a, T b) where T : IComparable<T> { a = a.CompareTo(b) < 0 ? b : a; }
    void chmin<T>(ref T a, T b) where T : IComparable<T> { a = a.CompareTo(b) < 0 ? a : b; }

    void solve()
    {
        int N = cin.nextint;
        var A = cin.scanlong;
        var B = cin.scanlong;

        if (A.Sum() < B.Sum())
        {
            WriteLine(-1);
            return;
        }

        var P = new PriorityQueue<long>();
        var M = new PriorityQueue<long>();
        for (int i = 0; i < N; i++)
        {
            if (A[i] < B[i])
            {
                M.Enqueue(B[i] - A[i]);
            }
            else if(A[i] > B[i])
            {
                P.Enqueue(A[i] - B[i]);
            }
        }

        long remain = 0;
        int ans = M.Count;
        while (M.Any())
        {
            var d = M.Dequeue();
            while (d > remain)
            {
                remain += P.Dequeue();
                ans++;
            }
            remain -= d;
        }

        WriteLine(ans);
    }


    class PriorityQueue<T> where T : IComparable<T>
    {
        List<T> heap; int size;
        int cmp = 1;
        int Compare(T x, T y) { return y.CompareTo(x); }
        public PriorityQueue() { heap = new List<T>(); }
        public PriorityQueue(int k) { heap = new List<T>(); cmp = k; }
        public void Enqueue(T x)
        {
            heap.Add(x);
            int i = size++;
            while (i > 0)
            {
                int p = (i - 1) >> 1;
                if (Compare(heap[p], x) * cmp <= 0) break;
                heap[i] = heap[p]; i = p;
            }
            heap[i] = x;
        }
        public T Dequeue()
        {
            T ret = heap[0]; T x = heap[--size];
            int i = 0;
            while ((i << 1) + 1 < size)
            {
                int a = (i << 1) + 1; int b = (i << 1) + 2;
                if (b < size && Compare(heap[b], heap[a]) * cmp < 0) a = b;
                if (Compare(heap[a], x) * cmp >= 0) break;
                heap[i] = heap[a]; i = a;
            }
            heap[i] = x; heap.RemoveAt(size);
            return ret;
        }
        public int Count { get { return size; } }
        public bool Any() { return size > 0; }
        public T Peek() { return heap[0]; }
    }
}

class Scanner
{
    string[] s; int i;
    readonly char[] cs = new char[] { ' ' };
    public Scanner() { s = new string[0]; i = 0; }
    public string[] scan { get { return ReadLine().Split(); } }
    public int[] scanint { get { return Array.ConvertAll(scan, int.Parse); } }
    public long[] scanlong { get { return Array.ConvertAll(scan, long.Parse); } }
    public double[] scandouble { get { return Array.ConvertAll(scan, double.Parse); } }
    public string next
    {
        get
        {
            if (i < s.Length) return s[i++];
            string st = ReadLine();
            while (st == "") st = ReadLine();
            s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
            i = 0;
            return next;
        }
    }
    public int nextint { get { return int.Parse(next); } }
    public long nextlong { get { return long.Parse(next); } }
    public double nextdouble { get { return double.Parse(next); } }
    public void join<T>(IEnumerable<T> values) { WriteLine(string.Join(" ", values)); }
}

Measured memory_bytes: 37980