The answer is: 5/3pi53π.
Every 2pi2π the angles repeat. So it is possible to add, or subtract, at one angle 2pi2π how many times you want.
Let's sum it until we "reach" an angle of "the first round", i.e until the angle is in [0,2pi][0,2π].
-55/3pi+2pi=-55/3pi+6/3pir=-49/3pi−553π+2π=−553π+63πr=−493π
-49/3pi+6/3pi=-43/3pi−493π+63π=−433π
-43/3pi+6/3pi=-37/3pi−433π+63π=−373π
-37/3pi+6/3pi=-31/3pi−373π+63π=−313π
-31/3pi-6/3pi=-25/3pi−313π−63π=−253π
-25/3pi+6/3pi=-19/3pi−253π+63π=−193π
-19/3pi+6/3pi=-13/3pi−193π+63π=−133π
-13/3pi+6/3pi=-7/3pi−133π+63π=−73π
-7/3pi+6/3pi=-pi/3−73π+63π=−π3
-pi/3+6/3pi=5/3pi−π3+63π=53π.