#include <bits/stdc++.h>
using namespace std;
const int INF = 2000000009;
const int Max = 1000007;
const double PI = acos(-1.0);
long long cnt[30];
int main() {
  double i, j, k, d, v1, v2, l, temp, t, n, m, caseno = 0, ans, N;
  while (cin >> d >> l >> v1 >> v2) {
    ans = (l - d) / (v1 + v2);
    printf("%.10lf\n", ans);
  }
  return 0;
}
