using System;
using System.Collections.Generic;
using System.Linq;
using static AtCoder;
using System.Threading.Tasks;
using System.ComponentModel;

public class Hello
{
    private const int INF = 1000000007;
    public static void Main()
    {
        int N = IntRead();
        long[] A = LongLine();
        long[] B = LongLine();

        long stack = 0;
        long ans = 0;
        for (int i = 0; i < N; i++)
        {
            if (A[i] < B[i]) { stack += (B[i] - A[i]); ans += 1; }
        }
        if (stack == 0) { Console.WriteLine(0); return; }
        Dictionary<long, long> bank = new Dictionary<long, long>();
        long stack_b = stack;
        for (int i = 0; i < N; i++)
        {
            if (A[i] > B[i])
            {
                bank[i] = (A[i] - B[i]);
                stack -= (A[i] - B[i]);
            }
        }
        //借金返せてない
        if (stack > 0) { Console.WriteLine(-1); return; }
        var sorted = bank.OrderByDescending(v => v.Value);
        foreach (var d in sorted)
        {
            ans++;
            stack_b -= d.Value;
            if (stack_b <= 0) break;
        }
        Console.WriteLine(ans);
    }
}

public class UnionFind
{
    public List<int> parent = new List<int>();

    public UnionFind(int N)
    {
        for (int i = 0; i < N; i++) parent.Add(i);
    }

    public int Find(int a)
    {
        if (parent[a] == a) return a;
        else return parent[a] = Find(parent[a]);
    }

    public void Unite(int a, int b)
    {
        a = Find(a);
        b = Find(b);
        if (a == b) return;
        parent[a] = parent[b];
    }

    public bool Same(int a, int b) { return (Find(a) == Find(b)); }
}
public class AtCoder
{
    public static void Swap<T>(ref T a, ref T b)
    {
        var t = a;
        a = b;
        b = t;
    }
    public static int GCD(int a, int b)
    {
        if (a < b) Swap(ref a, ref b);
        int d = a % b;
        while (b != 0)
        {
            d = a % b;
            a = b;
            b = d;
        }
        return a;
    }
    public static long LCM(int a, int b)
    {
        return (long)a * b / GCD(a, b);
    }
    public static string StrReverce(string s)
    {
        return new string(s.Reverse().ToArray());
    }
    public static int IntRead()
    {
        return int.Parse(Console.ReadLine());
    }
    public static bool IsPrime(int n)
    {
        if (n < 2) return false;
        if (n == 2) return true;
        if (n % 2 == 0) return false;

        //double sqrtNum = Math.Sqrt(n);
        for (int i = 3; i < n; i += 2)
        {
            if (n % i == 0) return false;
        }
        return true;
    }
    public static string[] SpRead(char c)
    {
        return Console.ReadLine().Split(c);
    }
    public static long[] LSRead()
    {
        return Console.ReadLine().Split(' ').Select(long.Parse).ToArray();
    }
    public static long Combination(int n, int r)
    {
        if (n == r || r == 0) return 1;
        return
            Enumerable.Range((n - r + 1), r).ToList().Aggregate((now, next) => now * next) /
            Enumerable.Range(1, r).ToList().Aggregate((now, next) => now * next);
    }
    public static long Permutation(int n, int r)
    {
        if (n == r) return 1;
        return
            Enumerable.Range((n - r), r).ToList().Aggregate((now, next) => now * next);
    }
    public static long RepPow(long x, long p, long m = 1000000007)
    {
        if (p == 1) return x % m;
        long b = RepPow(x, p / 2, m) % m;
        if (p % 2 == 0) { return (b * b) % m; }
        else { return (x * ((b * b) % m)) % m; }
    }
    public static long LongRead()
    {
        return long.Parse(Console.ReadLine());
    }
    public static long[] LongLine()
    {
        return Console.ReadLine().Split(' ').Select(long.Parse).ToArray();
    }
    public static int[] IntLine(int v = 0)
    {
        return Console.ReadLine().Split(' ').Select(int.Parse).Select(a => a + v).ToArray();
    }
}


Measured memory_bytes: 33632