#include <bits/stdc++.h>
using namespace std;
int a[26];
map<long long, int> m;
int main() {
  ios_base::sync_with_stdio(false);
  int d, L, v1, v2;
  cin >> d >> L >> v1 >> v2;
  cout << setprecision(20) << (double)(L - d) / (double)(v1 + v2);
  return 0;
}
