static double CalcDistance(ReadPoint p1, ReadPoint p2)
{
int a = p1.X - p2.X;
int b = p1.Y - p2.Y;
return(Math.Sqrt(a * a + b * b));
}
static void Main()
{
int[] input1 = Console.ReadLine().Split().Select(int.Parse).ToArray();
int[] input2 = Console.ReadLine().Split().Select(int.Parse).ToArray();
ReadPoint p1 = new ReadPoint {
X = input1[0], Y = input1[1]
};
ReadPoint p2 = new ReadPoint {
X = input2[0], Y = input2[1]
};
Console.WriteLine("{0:F3}", CalcDistance(p1, p2));
}
