#include <bits/stdc++.h>
using namespace std;
const int INF = 1E9 + 7;
vector<int> g[505];
int main() {
  double d, l, v1, v2;
  cin >> d >> l >> v1 >> v2;
  double tr = (l - d) / (v1 + v2);
  printf("%.6f", tr);
  return 0;
}
