#include<fstream>
#include<vector>
#include<string>

using namespace std;

ifstream fin("a.in");
ofstream fout("a.out");

string sir;
double t1,t2,k1,k2;

int main()
{
    cin >> t1>> k1>>t2>>k2;

    double sol = ((t1 / k1)+(t2/k2))/4;
    cout << sol <<"\n";

}