Private Sub Worksheet_Change(ByVal Target As Range)
Dim x As Variant
If Target.Address(False, False) = "B2" And Target.Value = "X(!)" Then
x = Application.InputBox("Enter amount", Type:=1)
If TypeName(x) = "Boolean" Then Exit Sub
Application.EnableEvents = False
Range("C2").Value = x
Application.EnableEvents = True
End If
End Sub