#include <bits/stdc++.h>
using namespace std;
double d, l, v1, v2;
int main() {
  ios_base::sync_with_stdio(0);
  cin >> d >> l >> v1 >> v2;
  cout << setprecision(8);
  cout << fixed << (l - d) / (v1 + v2) << "\n";
  return 0;
}
