#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e9;
int main() {
  double d, L, v, u;
  cin >> d >> L >> v >> u;
  double t = (L - d) / (v + u);
  cout.precision(11);
  cout << max(t, 0.0);
  return 0;
}
