Module P1
Sub main()

    Dim RD As String
    Dim SD() As String
    
    Dim AB As Long
    Dim BC As Long
    Dim ans As Long
    
    
    RD = Console.Readline()
    SD = Split(RD, " ")
    
    AB = SD(0)
    BC = SD(1)
    
    ans = AB * BC / 2
    
    Console.Writeline (ans)


End Sub

end Module
