Intro (Repeat twice):
E|---------------------------------------------------------|
B|-----------3-------------3-------------3---------1p0-----|
G|-----4-------------4-------------4-------------4-----2p0-|
D|---2-----2-------0-----0-------2-----2-------2-----------|
A|-----------------------------3-----3-----3-3-------------|
E|-0-----0-----0-3-----3-----3-----------------------------|

Rhianna and Katy Perry Part (and optional Beiber part at the end):

E|-----------------------------------------------------------|
B|-----------3-------------3-------------3-------------3-----|
G|-----4-------------4-------------4-------------4-----------|
D|---2-----2-------0-----0-------2-----2-------2-----2-------|
A|-----------------------------3-----3-----3-3-----3-----3---|
E|-0-----0-----0-3-----3-----3-------------------------------|

Lady Gaga Part:
E|-----------------------------------------------------------|
B|-----------------------------------------------------------|
G|-----------------------------------------------------------|
D|-----------------------------------------------------------|
A|-----------------------------3-------------3---------------|
E|-0-------------3-------------------------------------------|