问题1442--BUYING FEED

1442: BUYING FEED

时间限制: 1 Sec  内存限制: 128 MB
提交: 121  解决: 45
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题目描述

Farmer John needs to travel to town to pick up K (1 <= K <= 100)pounds of feed. Driving D miles with K pounds of feed in his truck costs D*K cents.
The county feed lot has N (1 <= N <= 100) stores (conveniently numbered 1..N) that sell feed. Each store is located on a segment of the X axis whose length is E (1 <= E <= 350). Store i is at
location X_i (0 < X_i < E) on the number line and can sell John as much as F_i (1 <= F_i <= 100) pounds of feed at a cost of C_i (1 <= C_i <= 1,000,000) cents per pound. Amazingly, a given point on the X axis might have more than one store.
Farmer John starts at location 0 on this number line and can drive only in the positive direction, ultimately arriving at location E, with at least K pounds of feed. He can stop at any of the feed stores along the way and buy any amount of feed up to the the store's limit.
What is the minimum amount Farmer John has to pay to buy and transport the K pounds of feed? Farmer John knows there is a solution.
Consider a sample where Farmer John needs two pounds of feed from three stores (locations: 1, 3, and 4) on a number line whose range is 0..5:
0 1 2 3 4 5
---------------------------------
1 1 1 Available pounds of feed
1 2 2 Cents per pound
It is best for John to buy one pound of feed from both the second and third stores. He must pay two cents to buy each pound of feed for a total cost of 4. When John travels from 3 to 4 he is moving 1 unit of length and he has 1 pound of feed so he must pay 1*1 = 1 cents.
When John travels from 4 to 5 he is moving one unit and he has 2 pounds of feed so he must pay 1*2 = 2 cents. The total cost is 4+1+2 = 7 cents.

输入

Line 1: Three space-separated integers: K, E, and N
Lines 2…N+1: Line i+1 contains three space-separated integers: Xi Fi Ci

输出

A single integer that is the minimum cost for FJ to buy and transport the feed

样例输入 Copy
2 5 3
3 1 2
4 1 2
1 1 1

样例输出 Copy
7
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