using System; using System.Collections.Generic; using System.Linq; using System.IO; using System.Text; using System.Numerics; namespace Solver { class Program { const int M = 1000000007; const double eps = 1e-9; static void Main() { var sw = new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false }; var sc = new Scan(); var p = sc.IntArr; var q = sc.IntArr; sw.WriteLine((p[1] * q[0] + p[0] * q[1]) / (double)(p[0] + q[0])); sw.Flush(); } static string strsort(string s) { var c = s.ToCharArray(); Array.Sort(c); return string.Join("", c); } static string strswap(string s, int i, int j) { var c = s.ToCharArray(); c[i] = s[j]; c[j] = s[i]; return string.Join("", c); } static T[] copy(T[] a) { var ret = new T[a.Length]; for (int i = 0; i < a.Length; i++) ret[i] = a[i]; return ret; } } class Scan { public int Int { get { return int.Parse(Console.ReadLine().Trim()); } } public long Long { get { return long.Parse(Console.ReadLine().Trim()); } } public string Str { get { return Console.ReadLine().Trim(); } } public int[] IntArr { get { return Console.ReadLine().Trim().Split().Select(int.Parse).ToArray(); } } public int[] IntArrWithSep(char sep) { return Console.ReadLine().Trim().Split(sep).Select(int.Parse).ToArray(); } public long[] LongArr { get { return Console.ReadLine().Trim().Split().Select(long.Parse).ToArray(); } } public double[] DoubleArr { get { return Console.ReadLine().Split().Select(double.Parse).ToArray(); } } public string[] StrArr { get { return Console.ReadLine().Trim().Split(); } } public List IntList { get { return Console.ReadLine().Trim().Split().Select(int.Parse).ToList(); } } public List LongList { get { return Console.ReadLine().Trim().Split().Select(long.Parse).ToList(); } } public void Multi(out int a, out int b) { var arr = IntArr; a = arr[0]; b = arr[1]; } public void Multi(out int a, out int b, out int c) { var arr = IntArr; a = arr[0]; b = arr[1]; c = arr[2]; } public void Multi(out int a, out int b, out int c, out int d) { var arr = IntArr; a = arr[0]; b = arr[1]; c = arr[2]; d = arr[3]; } public void Multi(out int a, out string b) { var arr = StrArr; a = int.Parse(arr[0]); b = arr[1]; } public void Multi(out int a, out int b, out string c) { var arr = StrArr; a = int.Parse(arr[0]); b = int.Parse(arr[1]); c = arr[2]; } public void Multi(out int a, out char b) { var arr = StrArr; a = int.Parse(arr[0]); b = arr[1][0]; } public void Multi(out char a, out int b) { var arr = StrArr; a = arr[0][0]; b = int.Parse(arr[1]); } public void Multi(out long a, out long b) { var arr = LongArr; a = arr[0]; b = arr[1]; } public void Multi(out long a, out int b) { var arr = LongArr; a = arr[0]; b = (int)arr[1]; } public void Multi(out string a, out string b) { var arr = StrArr; a = arr[0]; b = arr[1]; } } class mymath { const double eps = 1e-9; public long powmod(long a, long b, long M) { if (b == 0) return 1; if (b == 1) return a % M; var t = powmod(a, b / 2, M); if ((b & 1) == 0) return t * t % M; else return t * t % M * a % M; } public long gcd(long a, long b) { while (b != 0) { var t = a % b; a = b; b = t; } return a; } public long lcm(int a, int b) { return a * (long)b / gcd(a, b); } } }