Hi,
You can not do that in the UI Flow.
How would a user navigating to the entry point provide for the input parameter.
You can of course navigate to the entry point but you have to ensure that the parameter is set on the URL.
https://<yourenvironment/YourApp/Entry1.aspx?Input1=ValueForInput1
Like in above url the screen for Entry1 has a parameter called Input1 and the value will be set to ValueForInput1
Regards,
Daniel