#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5010;
const int mod = 1e9 + 7;
const int INF = 0x3f3f3f3f;
const double pi = acos(-1.0);
const double eps = 1e-4;
int main() {
  double d, l, v1, v2;
  cin >> d >> l >> v1 >> v2;
  printf("%.6lf\n", (l - d) / (v1 + v2));
  return 0;
}
