using System;

interface ITriangle

{ double Perimetar();

  double Face();

}

class Triangle1 : ITriangle

{   private double a,b,c;

    public Triangle1(double a, double b, double c)

    {this.a=a; this.b=b; this.c=c;

    }

    public double Perimetar()

    {return a+b+c;}

    public double Face()

    { double p=this.Perimetar()/2;

      return Math.Sqrt(p*(p-a)*(p-b)*(p-c));

    }

}

public class Program

{

    public static void Main()

    {

        Console.WriteLine("задача 1 стр.124 интерфейс ITriangle");

        Triangle1 t=new Triangle1(3,4,5);

        Console.WriteLine("Perimetar = {0} , Lice = {1}",t.Perimetar(), t.Face());

    }

}