Problem:
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Cross Points of Circles

For given two circles $c1$ and $c2$, print the coordinates of the cross points of them.

Input

The input is given in the following format.

$c1x\; c1y\; c1r$

$c2x\; c2y\; c2r$

$c1x$, $c1y$ and $c1r$ represent the coordinate and radius of the first circle.
$c2x$, $c2y$ and $c2r$ represent the coordinate and radius of the second circle.
All input values are given in integers.

Output

Print the coordinates ($x1$, $y1$) and ($x2$, $y2$) of the cross points $p1$ and $p2$ respectively in the following rules.

If there is one cross point, print two coordinates with the same values.

Print the coordinate with smaller $x$ first. In case of a tie, print the coordinate with smaller $y$ first.

The output values should be in a decimal fraction with an error less than 0.000001.

Constraints

The given circle have at least one cross point and have different center coordinates.

$-10,000 \leq c1x, c1y, c2x, c2y \leq 10,000$

$1 \leq c1r, c2r \leq 10,000$

Sample Input and Output

Sample Input 1

0 0 2
2 0 2

Sample Output 1

1.00000000 -1.73205080 1.00000000 1.73205080

Sample Input 2

0 0 2
0 3 1

Sample Output 2

0.00000000 2.00000000 0.00000000 2.00000000

Solution in C# (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            double[] input = Array.ConvertAll(Console.ReadLine().Split(' '), double.Parse);
            Circle c1 = new Circle(new Point(input[0], input[1]), input[2]);

            input = Array.ConvertAll(Console.ReadLine().Split(' '), double.Parse);
            Circle c2 = new Circle(new Point(input[0], input[1]), input[2]);

            KeyValuePair<Point, Point> temp = GetCrossPoints(c1, c2);
            if (temp.Key < temp.Value) Console.WriteLine(temp.Key + " " + temp.Value);
            else Console.WriteLine(temp.Value + " " + temp.Key);
        }

        static double Arg(Point p)
        {
            return Math.Atan2(p.y, p.x);
        }

        static Point Polar(double a, double r)
        {
            return new Point(Math.Cos(r) * a, Math.Sin(r) * a);
        }

        static KeyValuePair<Point, Point> GetCrossPoints(Circle c1, Circle c2)
        {
            double d = (c1.p - c2.p).Abs;
            double a = Math.Acos((c1.r * c1.r + d * d - c2.r * c2.r) / (2 * c1.r * d));
            double t = Arg(c2.p - c1.p);
            return new KeyValuePair<Point, Point>(c1.p + Polar(c1.r, t + a), c1.p + Polar(c1.r, t - a));
        }
    }

    class Point : IComparable<Point>
    {
        static readonly double EPS = 1E-10;

        internal double x, y;

        public Point(double x, double y)
        {
            this.x = x;
            this.y = y;
        }

        public double Abs { get { return Math.Sqrt(Norm); } }
        public double Norm { get { return x * x + y * y; } }

        public double Dot(Point p) { return x * p.x + y * p.y; }
        public double Cross(Point p) { return x * p.y - y * p.x; }

        public static Point operator +(Point a, Point b) { return new Point(a.x + b.x, a.y + b.y); }
        public static Point operator -(Point a, Point b) { return new Point(a.x - b.x, a.y - b.y); }
        public static Point operator *(Point p, double d) { return new Point(p.x * d, p.y * d); }
        public static Point operator /(Point p, double d) { return new Point(p.x / d, p.y / d); }
        public static bool operator <(Point a, Point b) { return Math.Abs(a.x - b.x) > EPS ? a.x < b.x : a.y < b.y; }
        public static bool operator >(Point a, Point b) { return Math.Abs(a.x - b.x) > EPS ? a.x > b.x : a.y > b.y; }
        public static bool operator ==(Point a, Point b) { return Math.Abs(a.x - b.x) < EPS && Math.Abs(a.y - b.y) < EPS; }
        public static bool operator !=(Point a, Point b) { return Math.Abs(a.x - b.x) >= EPS || Math.Abs(a.y - b.y) >= EPS; }

        public int CompareTo(Point other)
        {
            return x != other.x ? (int)(x - other.x) : (int)(y - other.y);
        }

        public override bool Equals(object obj)
        {
            Point other = obj as Point;
            return Math.Abs(x - other.x) < EPS && Math.Abs(y - other.y) < EPS;
        }

        public override int GetHashCode()
        {
            return x.GetHashCode() ^ y.GetHashCode();
        }

        public override string ToString()
        {
            return string.Format("{0:f10} {1:f10}", x, y);
        }
    }

    class Segment
    {
        internal Point p1, p2;

        public Segment(Point p1, Point p2)
        {
            this.p1 = p1;
            this.p2 = p2;
        }
    }

    class Circle
    {
        internal Point p;
        internal double r;

        public Circle(Point p, double r)
        {
            this.p = p;
            this.r = r;
        }
    }
}