#include <cstdio>
#include <cmath>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
#define rt(x) ((x)*(x))

int xa,ya;
int xb,yb;
int main(void){
  cin >> xa >> ya >> xb >> yb;
  if(ya > yb){
    swap(xa,xb);
    swap(ya,yb);
  }

  double p = ya+(yb-ya)*(((double)xa/(double)(xa+xb)));
  cout << p << endl;

  //cout << sqrt(rt(xa)+rt(p-ya)) + sqrt(rt(xb)+rt(p-yb)) << endl;
}