#include<iostream>
#include<stdio.h>
using namespace std;

#pragma warning(push)
#pragma warning(disable: 4996)

#define NMAX 100005

int v1, v2, k1, k2;

int main()
{
	//freopen("mindcoding.in", "r", stdin);
	//freopen("mindcoding.out", "w", stdout);
	
	cin >> v1 >> v2 >> k1 >> k2;

	cout << 100 / (double)(v1 * k1 + v2 * k2);


	return 0;
}

#pragma warning(pop)