#include <bits/stdc++.h>
using namespace std;
int main() {
  double d, l, v1, v2;
  cin >> d >> l >> v1 >> v2;
  double res = (l - d) / (v1 + v2);
  cout.setf(ios::fixed | ios::showpoint);
  cout.precision(10);
  cout << res << '\n';
}
