﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TriangleSurfaceBySideAndAltitude {

  class Triangulo {

    private double h;

    public double N {private set;get;}
    public double H {
      set {
        this.h = value;
      } 
      get {
        return h;
      }
    }

    public Triangulo(double n, double h) {
      this.N = n;
      this.H = h;
    }

    public Triangulo() {
      this.N = 0;
      this.H = 0;
    }

    public void SetN(double n) {
      this.N = n;
    }

    public double CalcularAreaTriangulo(double n, double h) {
      double area = (n*h)/2;
      return area;
    }

}

  
  class Program {
    static void Main(string[] args) {

      double n = double.Parse(Console.ReadLine());
      double h = double.Parse(Console.ReadLine());

      Triangulo triangulo = new Triangulo(n,h);
      double area = triangulo.CalcularAreaTriangulo(triangulo.N, triangulo.H);

      Console.WriteLine("{0:0.00}",area);

      }
  }
}
