Luke Skywalker got locked up in a rubbish shredder between two presses. R2D2 is already working on his rescue, but Luke needs to stay alive as long as possible. For simplicity we will assume that everything happens on a straight line, the presses are initially at coordinates 0 and L, and they move towards each other with speed v1 and v2, respectively. Luke has width d and is able to choose any position between the presses. Luke dies as soon as the distance between the presses is less than his width. Your task is to determine for how long Luke can stay alive.

Input

The first line of the input contains four integers d, L, v1, v2 (1 ≤ d, L, v1, v2 ≤ 10 000, d < L) — Luke's width, the initial position of the second press and the speed of the first and second presses, respectively.

Output

Print a single real value — the maximum period of time Luke can stay alive for. Your answer will be considered correct if its absolute or relative error does not exceed 10 - 6. 

Namely: let's assume that your answer is a, and the answer of the jury is b. The checker program will consider your answer correct, if <image>.

Examples

Input

2 6 2 2


Output

1.00000000000000000000


Input

1 9 1 2


Output

2.66666666666666650000

Note

In the first sample Luke should stay exactly in the middle of the segment, that is at coordinates [2;4], as the presses move with the same speed.

In the second sample he needs to occupy the position <image>. In this case both presses move to his edges at the same time.
//package com.company;
import com.sun.nio.sctp.SctpStandardSocketOptions;
import javax.swing.*;
import java.math.BigInteger;
import java.util.Calendar;
import java.net.StandardSocketOptions;
import java.util.*;
import java.util.Calendar;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.text.SimpleDateFormat;
import java.util.Arrays;
import java.util.Calendar;
import java.util.Random;
import java.util.StringTokenizer;
import java.io.*;
import java.util.ArrayList;
import java.math.BigInteger;
    /*
                                                DOMINGO_GIRL :)
                                                ─────────▄──────────────▄
                                                ────────▌▒█───────────▄▀▒▌
                                                ────────▌▒▒▀▄───────▄▀▒▒▒▐
                                                ───────▐▄▀▒▒▀▀▀▀▄▄▄▀▒▒▒▒▒▐
                                                ─────▄▄▀▒▒▒▒▒▒▒▒▒▒▒█▒▒▄█▒▐
                                                ───▄▀▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▀██▀▒▌
                                                ──▐▒▒▒▄▄▄▒▒▒▒▒▒▒▒▒▒▒▒▒▀▄▒▒▌
                                                ──▌▒▒▐▄█▀▒▒▒▒▄▀█▄▒▒▒▒▒▒▒█▒▐
                                                ─▐▒▒▒▒▒▒▒▒▒▒▒▌██▀▒▒▒▒▒▒▒▒▀▄▌
                                                ─▌▒▀▄██▄▒▒▒▒▒▒▒▒▒▒▒░░░░▒▒▒▒▌
                                                ─▌▀▐▄█▄█▌▄▒▀▒▒▒▒▒▒░░░░░░▒▒▒▐ Wow
                                                ▐▒▀▐▀▐▀▒▒▄▄▒▄▒▒▒▒▒░░░░░░▒▒▒▒▌
                                                ▐▒▒▒▀▀▄▄▒▒▒▄▒▒▒▒▒▒░░░░░░▒▒▒▐
                                                ─▌▒▒▒▒▒▒▀▀▀▒▒▒▒▒▒▒▒░░░░▒▒▒▒▌
                                                ─▐▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▐
                                                ──▀▄▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▄▒▒▒▒▌
                                                ────▀▄▒▒▒▒▒▒▒▒▒▒▄▄▄▀▒▒▒▒▄▀
                                                ───▐▀▒▀▄▄▄▄▄▄▀▀▀▒▒▒▒▒▄▄▀
                                                ──▐▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▀▀
                                            */

    public class Main {
        static final int mod = (int)1e9+7;
        public static void main(String[] arg) {
            Scanner sc = new Scanner(System.in);
            int d=sc.nextInt();int l=sc.nextInt();int v1=sc.nextInt();int v2=sc.nextInt();
            System.out.println((double) (l-d)/(v1+v2));

        }

        //find the summation from 1 to n
        public static int from1toN(long n){
            int s=0;
            for(int i=1;i<=n;i++){
                s+=i;
            }
            return s;
        }

        static long nCr(long N, long K)		// O(K)
        {
            if(K > N)
                return 0;
            long res = 1;
            for(int i = 1; i <= K; ++i)
                res = (N - K + i) * res / i;
            return res;
        }

        static long nCr2(long n, long r)
        {
            return fact(n) / (fact(r) *
                    fact(n - r));
        }

        // Returns factorial of n
        static long fact(long n)
        {
            int res = 1;
            for (int i = 2; i <= n; i++)
                res = res * i;
            return res;
        }




        public static int CharOccurrences(ArrayList<String>h,int k){
            int count=0;int c=0;
            for(int i=0;i<h.size();i++){
                count=0;
                for(int j=0;j<h.get(i).length();j++){
                    if(h.get(i).charAt(j)=='1')count++;
                }
                if(count==k)c++;
            }
              return c;
        }


        static void recursiveReverse(int[] a, int i)
        {
            int n = a.length;
            if (i == n / 2)
                return;
            swap(a,i,n - i - 1);
            recursiveReverse(a, i + 1);
        }

        static int[] swap(int []arr, int i, int j)
        {
            int temp= arr[i];
            arr[i]=arr[j];
            arr[j]=temp;
            return arr;
        }


        //Knapsack Problem
        public static double knapsackGreedySolution(double profit[],double weight[],int n,int w) {
            double P_W[] = new double[n];
            for (int i = 0; i < n; i++) P_W[i] = (double) profit[i] / (double) weight[i];

            for (int i = 0; i < n - 1; i++) {
                for (int j = i + 1; j < n; j++) {
                    if (P_W[i] < P_W[j]) {
                        double temp = P_W[i];
                        P_W[i] = P_W[j];
                        P_W[j] = temp;

                        double temp2 = profit[i];
                        profit[i] = profit[j];
                        profit[j] = temp2;

                        double temp3 = weight[i];
                        weight[i] = weight[j];
                        weight[j] = temp3;
                    }
                }
            }
            int k = 0;
            double sum = 0;
            while (w > 0) {

                if (weight[k] < w) {
                    sum += profit[k];
                    w -= weight[k];
                } else {
                    sum += (w * profit[k]) / weight[k];
                    w = 0;
                }
                k++;
            }
            return  sum;
        }


        static boolean isPrime(int n)
        {
            // Corner cases
            if (n <= 1) return false;
            if (n <= 3) return true;

            // This is checked so that we can skip
            // middle five numbers in below loop
            if (n % 2 == 0 || n % 3 == 0) return false;

            for (int i = 5; i * i <= n; i = i + 6)
                if (n % i == 0 || n % (i + 2) == 0)
                    return false;

            return true;
        }


        public static boolean checkSegment(int a,int b,int c){

            // check condition
            if (a + b == c || a + c == b || b + c == a)
                return true;
            else
                return false;
        }


        // Function to calculate for validity
        public static boolean checkValidity(int a,
                                        int b, int c)
        {
            // check condition
            if (a + b > c && a + c > b && b + c > a)
                return true;
            else
                return false;
        }

        // Function to convert the obtained fraction
        // into it's simplest form
        static String lowest(int p,int d)
        {
            // Finding gcd of both terms
            int common_factor = gcd(p, d);

            // Converting both terms into simpler
            // terms by dividing them by common factor
            d = d / common_factor;
            p = p / common_factor;

            return p+"/"+d;
        }
        // Function to return gcd of a and b
        static int gcd(int a, int b)
        {
            if (a == 0)
                return b;
            return gcd(b % a, a);
        }


    }


