UVa 10250 - The Other Two Trees

#include <stdio.h>
#include <math.h>
#include <iostream>
#include <iomanip>

using namespace std;

const double e  = 1e-9;

int main()
{
  double x1,y1,x2,y2;
  double ax1, ay1, ax2, ay2;

  while (cin>>x1>>y1>>x2>>y2)
  {
    if (fabs(x1-x2) < e && fabs(y1-y2)< e )
    {
      cout<<"Impossible."<<endl;
      continue;
    }

    ax1 = (x2 + x1 + y2 - y1) / 2;
    ay1 = (y2 + y1 + x1 - x2) / 2;
    ax2 = (x2 + x1 + y1 - y2) / 2;
    ay2 = (y2 + y1 + x2 - x1) / 2;

    cout<<fixed<<setprecision(10)<<ax1<<" "<<ay1<<" "<<ax2<<" "<<ay2<<endl;
}

  return 0;
}