#include <bits/stdc++.h>
using namespace std;
int main() {
  double d, l, v1, v2;
  cin >> d >> l >> v1 >> v2;
  double s = l - d;
  double a_v = v1 + v2;
  cout << setprecision(20) << fixed << s / a_v << endl;
  return 0;
}
