#include <bits/stdc++.h>
using namespace std;
int main() {
  int d, l, v1, v2;
  int c = 1;
  int x = 0;
  cin >> d >> l >> v1 >> v2;
  int up = l - d;
  int down = v1 + v2;
  cout << up / down;
  up %= down;
  if (up % down != 0) {
    cout << ".";
  }
  if (up % down == 0) {
    return 0;
  }
loop:
  while (up < down && up != 0) {
    up *= 10;
    x++;
    if (x != 1) cout << 0;
  }
  cout << up / down;
  c++;
  x = 0;
  up %= down;
  if (c == 15) {
    return 0;
  }
  goto loop;
  return 0;
}
