#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  vector<int> x(2), y(2);
  REP (i, 2)
    cin >> x[i] >> y[i];

  if (y[0] > y[1]) {
    swap(x[0], x[1]);
    swap(y[0], y[1]);
  }
  
  double ret = 1.0 * x[0] / (x[0] + x[1]) * abs(y[0] - y[1]) + y[0];
  cout << fixed << setprecision(12) << ret << endl;
  
  return 0;
}