I calculated : level 1 ~ level 678 sum : 1,354 stars, 2 stars needed to unlock the next area(114).
the picture : 14 stars needed, like one area more needed...
(This account, sksk592409) If this says that 'You need n stars to unlock this area...', it would be 1~6 stars and I could get, but now, this requires 14 stars.