How do I make it so my code runs everytime I click on a certain worksheet.

This is my code so far.

Sub TripsCopy()
Dim Trips As Integer
Dim tr As Integer

Active.Sheet (Expense)
Trips = InputBox("Enter Number of Trips Taken")
If Trips 1 Then
'Sheets("Individual Trip").Select
For tr = 1 To Trips
Sheets("Individual Trip").Copy After:=Sheets(Sheets.Count)
Next
End If
End Sub