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#3784

Bookshelf (Silver) 1s 128MB

Problems

Problem 2: Bookshelf (Silver) [Neal Wu / Traditional, 2012]

When Farmer John isn't milking cows, stacking haybales, lining up his cows,

or building fences, he enjoys sitting down with a good book. Over the

years, he has collected N books (1 <= N <= 2,000), and he wants to build

a new set of bookshelves to hold them all.

Each book i has a width W(i) and height H(i). The books need to be added

to a set of shelves in order; for example, the first shelf should contain

books 1...k for some k, the second shelf should start with book k+1, and so

on. Each shelf can have a total width of at most L (1 <= L <=1,000,000,000).

The height of a shelf is equal to the height of the

tallest book on that shelf, and the height of the entire set of bookshelves

is the sum of the heights of all the individual shelves, since they are all

stacked vertically.

Please help FJ compute the minimum possible height for the entire set of

bookshelves.

PROBLEM NAME: bookshelf


Input

* Line 1: Two space-separated integers: N and L.

* Lines 2..1+N: Line i+1 contains two space-separated integers: H(i)

and W(i). (1 <= H(i) <= 1,000,000; 1 <= W(i) <= L).


Output

* Line 1: The minimum possible total height for the set of bookshelves.


Example

5 10
5 7
9 2
8 5
13 2
3 8
21

INPUT DETAILS:

There are 5 books. Each shelf can have total width at most 10.

OUTPUT DETAILS:

There are 3 shelves, the first containing just book 1 (height 5, width 7),

the second containing books 2..4 (height 13, width 9), and the third

containing book 5 (height 3, width 8).


Source

USACO 2012 US Open Silver

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