#include <bits/stdc++.h>
const double EPS = 1e-10;
using namespace std;
inline long long rit() {
  long long f = 0, key = 1;
  char c;
  do {
    c = getchar();
    if (c == '-') key = -1;
  } while (c < '0' || c > '9');
  do {
    f = f * 10 + c - '0';
    c = getchar();
  } while (c >= '0' && c <= '9');
  return f * key;
}
void init() {}
double v, v2, d, L;
void read() { d = rit(), L = rit(), v = rit(), v2 = rit(); }
void solve() { printf("%.9f\n", (L - d) / (v + v2)); }
int main() {
  int nn = 1;
  init();
  while (nn--) {
    read();
    solve();
  }
  return 0;
}
