Module _20190422

    Sub Main()

        Dim sRead As String = Console.ReadLine()

        Dim iAB As Integer = sRead.Split(" ")(0)
        Dim iBC As Integer = sRead.Split(" ")(1)
        Dim iCA As Integer = sRead.Split(" ")(2)

        Console.WriteLine((iAB * iBC) / 2)

    End Sub

End Module