#include <bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;
const double PI = acos(-1.0);
long long a[5];
bool can(long long x) {
  long long s = a[2] + a[3] - 2 * x;
  return a[1] - 2 * s >= x;
}
int main() {
  double d, l, v1, v2;
  cin >> d >> l >> v1 >> v2;
  printf("%.9f", (l - d) / (v1 + v2));
}
