using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(Pente(20, 19, 21, 17));

        Console.WriteLine(Pente(20, 19, 21, 15));

    }

    public static double Pente (double xA, double yA, double xB, double yB)

    {

        return (yB - yA) / (xB - xA);

    }

}