using AtCoderBeginnerContest144.Questions;
using AtCoderBeginnerContest144.Extensions;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

namespace AtCoderBeginnerContest144.Questions
{
    public class QuestionE : AtCoderQuestionBase
    {
        public override IEnumerable<object> Solve(TextReader inputStream)
        {
            var nk = inputStream.ReadLongArray();
            var k = nk[1];
            var a = inputStream.ReadLongArray();
            var f = inputStream.ReadLongArray();
            
            Array.Sort(a);      // コスト低い順
            Array.Sort(f);
            Array.Reverse(f);   // コスト重い順。i番目のメンバーがFiを食べる

            var bestResult = BoundaryBinarySearch(result =>
            {
                long trainingCount = 0;
                for (int i = 0; i < a.Length; i++)
                {
                    var cost = a[i] * f[i];
                    if (a[i] * f[i] > result)
                    {
                        trainingCount += (long)Math.Ceiling((double)(a[i] * f[i] - result) / f[i]);
                    }
                }
                return trainingCount <= k;
            }, -1, a[a.Length - 1] * f[0]);

            yield return bestResult;
        }

        private static long BoundaryBinarySearch(Predicate<long> predicate, long ng, long ok)
        {
            // めぐる式二分探索
            // Span.BinarySearchだとできそうでできない（lower_boundがダメ）
            while (Math.Abs(ok - ng) > 1)
            {
                long mid = (ok + ng) / 2;

                if (predicate(mid))
                {
                    ok = mid;
                }
                else
                {
                    ng = mid;
                }
            }
            return ok;
        }

    }
}


namespace AtCoderBeginnerContest144
{
    class Program
    {
        static void Main(string[] args)
        {
            IAtCoderQuestion question = new QuestionE();    // 問題に合わせて書き換え
            var answers = question.Solve(Console.In);
            foreach (var answer in answers)
            {
                Console.WriteLine(answer);
            }
        }
    }
}

#region Base Classes

namespace AtCoderBeginnerContest144.Questions
{

    public interface IAtCoderQuestion
    {
        IEnumerable<object> Solve(string input);
        IEnumerable<object> Solve(TextReader inputStream);
    }

    public abstract class AtCoderQuestionBase : IAtCoderQuestion
    {
        public IEnumerable<object> Solve(string input)
        {
            var stream = new MemoryStream(Encoding.Unicode.GetBytes(input));
            var reader = new StreamReader(stream, Encoding.Unicode);

            return Solve(reader);
        }

        public abstract IEnumerable<object> Solve(TextReader inputStream);
    }

}

#endregion

#region Extensions

namespace AtCoderBeginnerContest144.Extensions
{
    internal static class TextReaderExtensions
    {
        internal static int ReadInt(this TextReader reader) => int.Parse(ReadString(reader));
        internal static long ReadLong(this TextReader reader) => long.Parse(ReadString(reader));
        internal static double ReadDouble(this TextReader reader) => double.Parse(ReadString(reader));
        internal static string ReadString(this TextReader reader) => reader.ReadLine();

        internal static int[] ReadIntArray(this TextReader reader, char separator = ' ') => ReadStringArray(reader, separator).Select(int.Parse).ToArray();
        internal static long[] ReadLongArray(this TextReader reader, char separator = ' ') => ReadStringArray(reader, separator).Select(long.Parse).ToArray();
        internal static double[] ReadDoubleArray(this TextReader reader, char separator = ' ') => ReadStringArray(reader, separator).Select(double.Parse).ToArray();
        internal static string[] ReadStringArray(this TextReader reader, char separator = ' ') => reader.ReadLine().Split(separator);
    }
}

#endregion

Measured memory_bytes: 40540