using System;

    interface ITriangle

    { double Perimeter();

     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 Perimeter()

     { return a + b +c; }

      public double Face()

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

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

      }

     }

public class Program

{

    public static void Main(string[] args)

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

     Console.WriteLine(" Perimeter {0}, Face {1}.", t.Perimeter(), t.Face());

    }

    }

​