#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;

int main(){
   int ax,ay,bx,by;
   cin >> ax >> ay >> bx >> by;
   cout << setprecision(10) << abs(by - ay) * min(ax,bx) / (ax + bx) + min(ay,by) << endl;
}