#include <bits/stdc++.h>
using namespace std;
const int maxN = 1e5 + 100;
int main() {
  double v, d, l, v1, v2;
  cin >> d >> l >> v1 >> v2;
  l -= d;
  v = v1 + v2;
  double x = l / v;
  printf("%.10f\n", x);
}
