#include <bits/stdc++.h>
using namespace std;
void prepare() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
}
int main() {
  long double d, l, v1, v2;
  cin >> d >> l >> v1 >> v2;
  long double ans = (l - d) / (v1 + v2);
  cout << fixed << setprecision(10) << ans << endl;
  return 0;
}
