#include <bits/stdc++.h>
const long long mxn = 1e5 + 7;
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long d, l, v1, v2;
  double ans = 0, sum = 0, mi = 0;
  cin >> d >> l >> v1 >> v2;
  mi = l - d;
  sum = v1 + v2;
  ans = mi / sum;
  cout << fixed << setprecision(19) << ans;
  return 0;
}
