#include <bits/stdc++.h>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int ax, ay, bx, by;
  cin >> ax >> ay >> bx >> by;
  if (ay > by) swap(ay, by), swap(ax, bx);
  cout << fixed << setprecision(10) << (double)(by - ay) / (ax + bx) * ax + ay << '\n';
  return 0;
}