Imports System.Collections.Generic
Imports System.Console

Module Program
    Sub Main()
        Dim q As Long = NextInt()
        Dim h As Long = NextInt()
        Dim s As Long = NextInt()
        Dim d As Long = NextInt()
        Dim n As Long = NextInt()

        For Each v As Long In New Long() {4 * q, 2 * h}
            s = Math.Min(s, v)
        Next

        WriteLine(Math.Min(2 * s, d) * (n \ 2) + s * (n Mod 2))
    End Sub

    Function NextInt() As Integer
        Return CInt(NextString())
    End Function

    Function NextString() As String
        Dim result As New List(Of Char)
        Do
            Dim tmp As Integer = Read()
            If tmp < 0 Then Exit Do
            Dim nextChar As Char = Chr(tmp)

            If Not Char.IsWhiteSpace(nextChar) Then
                result.Add(nextChar)
            ElseIf nextChar <> vbCr Then
                Exit Do
            End If
        Loop
        Return New String(result.ToArray())
    End Function
End Module
