Farmer John has received a shipment of N large hay bales (1≤N≤100,000), and placed them at various locations along the road leading to his barn. Unfortunately, he completely forgets that Bessie the cow is out grazing along the road, and she may now be trapped within the bales!

Each bale j has a size Sj and a position Pj giving its location along the one-dimensional road. Bessie the cow can move around freely along the road, even up to the position at which a bale is located, but she cannot cross through this position. As an exception, if she runs in the same direction for D units of distance, she builds up enough speed to break through and permanently eliminate any hay bale of size strictly less than D. Of course, after doing this, she might open up more space to allow her to make a run at other hay bales, eliminating them as well.

Bessie can escape to freedom if she can eventually break through either the leftmost or rightmost hay bale. Please compute the total area of the road consisting of real-valued starting positions from which Bessie cannot escape.

农民约翰收到了N个干草包(1≤N≤100000)，并将它们放置在一条道路上的

不同位置。不幸的是，他忘记了贝西是沿着道路放牧，她现在可能被困在干

草包里了！

每个包有一个大小Sj和位置Pj。贝西可以沿着道路自由走动，甚至可以

到达一捆草包所在的位置，但她必须通过这个位置。如果她向同一方向跑D单

位的距离，她就可以突破大小严格小于D的干草包。当然，这样做后她就可以

开发出更广阔的空间，突破其他干草包。

如果贝西可以突破最左边或最右边的干草包，她就可以重获新生。请计

算贝西无法逃脱的道路的面积。