#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,tune=native")
#pragma GCC optimize("fast-math")
#pragma warning(disable : 4996)
using namespace std;
const int MAXN = 100001;
const int inf = 1000000000;
const long double INF = 1.0 / 0.0;
const long double EPS = 1e-7;
const int mod = inf + 7;
const long double PI = acos(-1.0);
signed main() {
  ios_base::sync_with_stdio(0);
  cout.tie(0);
  cin.tie(0);
  ;
  long double d, l, v1, v2;
  cin >> d >> l >> v1 >> v2;
  cout << fixed << (l - d) / (v1 + v2);
}
