#include <bits/stdc++.h>
using namespace std;
int main() {
  double d, L, v1, v2;
  cin >> d >> L >> v1 >> v2;
  double t = 0;
  t = (double)((L - d) / (v1 + v2));
  cout.precision(16);
  cout << t;
  return 0;
}
