a = Range("A2:A" & [A65000].End(xlUp).Row)
Set MonDico1 = CreateObject("Scripting.Dictionary")
For Each c In a
MonDico1(c) = ""
Next c
b = Range("B2:B" & [B65000].End(xlUp).Row)
Set MonDico2 = CreateObject("Scripting.Dictionary")
For Each c In b
If Not MonDico1.exists(c) Then MonDico2(c) = ""
Next c
[F2].Resize(MonDico2.Count, 1) = Application.Transpose(MonDico2.keys)