#include <bits/stdc++.h>
#define NMAX 10005
#define MOD 666013
#define INF 0x3f3f3f3f
#define x first
#define y second
#define ll long long

using namespace std;

int main() {
	double v1,v2,k1,k2;

	cin>>v1>>v2>>k1>>k2;

	v1/=k1;
	v2/=k2;

	cout<<fixed<<setprecision(5)<<v1+v2;

	return 0;
}