## USACO 2013 December Contest, Gold

## Problem 2. Optimal Milking

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Problem 2: Optimal Milking [Brian Dean, 2013]
Farmer John has recently purchased a new barn containing N milking machines
(1 <= N <= 40,000), conveniently numbered 1..N and arranged in a row.
Milking machine i is capable of extracting M(i) units of milk per day (1 <=
M(i) <= 100,000). Unfortunately, the machines were installed so
close together that if a machine i is in use on a particular day, its two
neighboring machines cannot be used that day (endpoint machines have only
one neighbor, of course). Farmer John is free to select different subsets
of machines to operate on different days.
Farmer John is interested in computing the maximum amount of milk he can
extract over a series of D days (1 <= D <= 50,000). At the beginning of
each day, he has enough time to perform maintenance on one selected milking
machine i, thereby changing its daily milk output M(i) from that day forward.
Given a list of these daily modifications, please tell Farmer John how much
milk he can produce over D days (note that this number might not fit into a
32-bit integer).
PROBLEM NAME: optmilk
INPUT FORMAT:
* Line 1: The values of N and D.
* Lines 2..1+N: Line i+1 contains the initial value of M(i).
* Lines 2+N..1+N+D: Line 1+N+d contains two integers i and m,
indicating that Farmer John updates the value of M(i) to m at
the beginning of day d.
SAMPLE INPUT (file optmilk.in):
5 3
1
2
3
4
5
5 2
2 7
1 10
INPUT DETAILS:
There are 5 machines, with initial milk outputs 1,2,3,4,5. On day 1,
machine 5 is updated to output 2 unit of milk, and so on.
OUTPUT FORMAT:
* Line 1: The maximum total amount of milk FJ can produce over D days.
SAMPLE OUTPUT (file optmilk.out):
32
OUTPUT DETAILS:
On day one, the optimal amount of milk is 2+4 = 6 (also achievable as
1+3+2). On day two, the optimal amount is 7+4 = 11. On day three, the
optimal amount is 10+3+2=15.

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