static double Calculate(Tochki a, Tochki b)
{
int formulaX = Math.Abs(a.TochkaX1 - a.TochkaX2);
int formulaY = Math.Abs(a.TochkaY1 - a.TochkaY2);
double distance = Math.Sqrt(formulaX * formulaX + formulaY * formulaY);
return(distance);
}
static void Main(string[] args)
{
int[] rowFirst = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
int[] rowSecond = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
Tochki pointsFirstRow = new Tochki();
pointsFirstRow.TochkaX1 = rowFirst[0];
pointsFirstRow.TochkaY1 = rowFirst[1];
Tochki pointsSecondRow = new Tochki();
pointsFirstRow.TochkaX2 = rowSecond[0];
pointsFirstRow.TochkaY2 = rowSecond[1];
Console.WriteLine($"{Calculate(pointsFirstRow, pointsSecondRow):F3}");
}