#include <bits/stdc++.h>
using namespace std;
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  double d, L, v1, v2;
  cin >> d >> L >> v1 >> v2;
  double distance;
  int i, r;
  cout << fixed << setprecision(20) << (L - d) / (v1 + v2);
  return 0;
}
