Last 3 months sales sum without consider year

[Ratmadeep]

(Year) (month) (New Sales) (Roiling 3 Months) (Desired Value)
2020 jan 100 100 100
2020 feb 200 300 300
2020 mar 200 500 500
2020 apr 300 700 700
2020 may 400 900 900
2020 jun 400 1100 1100
2020 jul 600 1400 1400
2020 aug 600 1600 1600
2020 sep 600 1800 1800
2020 oct 100 1300 1300
2020 nov 100 800 800
2020 dec 520 720 720
2021 jan 100 100 720
2021 feb 450 550 1070
2021 mar 450 1000 1000
2021 apr 450 1350 1350
2021 may 450 1350 1350
2021 jun 200 1100 1100
2021 jul 500 1150 1150
2021 aug 500 1200 1200
2021 sep 500 1500 1500
2021 oct 500 1500 1500
2021 nov 450 1450 1450
2021 dec 800 1750 1750

How I can achieve the desired value field?