Advance Grade Calculation in Moodle

I wan to add this calculation method into my Moodle Course: I have 3 Quizes: First Two Quizes are optional/not mandatory (no failure) Quiz 1 & Quiz 2 **optional>>it will be added to overall course score if it is less than 100, each quiz total mark=1) Quiz 3 (The main course exam with total mark=100) Basically want to count score the course from quiz 3 i.e. main score and if total of this test is less than full marks, then it should be added from quiz 1 and 2 which are option to check if student has overall scored 100 or not I need to solve this ASAP Thank you