1.3.1 Mixing Milk

The Merry Milk makers company buys Milk from farmers, packages it to attractive 1-and 2-unit bottles, and then sells th At milk to grocery stores so we can each start we have with delicious cereal and milk.

Since milk packaging is such a difficult business in which to make money, it's important to keep the costs as low as poss Ible. Help Merry Milk makers purchase the Farmers ' Milk in the cheapest possible manner. The MMM company has a extraordinarily talented marketing department and knows precisely how much milk they need to their customers.

The company have contracts with several farmers from whom they could purchase milk, and each farmer have a (potentially) Diffe Rent price @ which they sell milk to the packing plant. Of course, a herd of cows can only produce so much milk each day, so the farmers already know how much milk they would have Available.

Each day, the Merry Milk makers can purchase an integer number of units of Milk from each farmer, a number that's always less than or equal to the farmer ' s limit (and might is the entire production from this farmer, none of the production, or any Integer in between).

Given:

• The Merry Milk makers ' daily requirement of Milk
• The cost per unit of milk from each farmer
• The amount of milk available from each farmer

Calculate the minimum amount of money, Merry Milk makers must spend to meet their daily need for Milk.

Note:the total milk produced per day by the farmers would always being sufficient to meet the demands of the Merry milk Maker s even if the prices is high.

Program Name:milk

INPUT FORMAT

line 1:	two integers, N and m.  the First value, N, (0 <= N <= 2,000,000) is the amount of milk that Merry milk makers wants per day.  the second, M, (0 <= M <= 5,000) is the number of farmers that they may buy from.
Lines 2 through M+1:	The next M lines each contain the integers:pI and Ai. PI (0 <= Pi <=) is the price of cents that farmer I charges. AI (0 <= Ai <= 2,000,000) is the amount of milk that farmer I can sell to Merry milk makers per day.

SAMPLE INPUT (file milk.in)

100 5

5 20

9 40

3 10

8 80

6 30

INPUT explanation

5 --MMM wants units of milk from 5 farmers

5 --Farmer 1 says, "I can sell units at 5 cents per unit"

9 etc.

3 --Farmer 3 says, "I can sell units at 3 cents per unit"

8 etc.

6 --Farmer 5 says, "I can sell units at 6 cents per unit"

OUTPUT FORMAT

A single, with a single integer, that's the minimum cost, Merry Milk makers Msut pay for one day ' s Milk.

SAMPLE OUTPUT (file milk.out)

630

OUTPUT explanation

Here's how the MMM company spent only 630 cents to purchase units of milk:

price per unit	Units < Span class= "S1" > available	Units bought	price * # units	total cost	Notes
5	20	20	5*20	100
9	40	0			Bought no milk from farmer 2
3	10	10	3*10	30
8	80	40	8*40	320	did not buy all units!
6	30		6*30	180
Total	180	100		630	Cheapest Total Cost

Code:

1#include <iostream>2#include <cstdio>3#include <cstring>4#include <algorithm>5 using namespacestd;6 structQ7 {8     Long LongP,a;9}v[5005];Ten BOOLCMP (q x,q y) One { A     returnx.p<Y.P; - } - intMain () the { -Freopen ("milk.in","R", stdin); -Freopen ("Milk.out","W", stdout); -     Long Longn,m; +Cin>>n>>m; -      for(intI=0; i<m;i++){ +Cin>>v[i].p>>v[i].a; A     } atSort (v,v+m,cmp); -     Long Longsum=0; -     Long LongPr=0; -      for(Long LongI=0; i<m&&sum<n;i++){ -         if(sum+v[i].a<N) { -sum+=v[i].a; inpr+=v[i].p*v[i].a; -         } to         Else { +pr+=v[i].p* (nsum); -sum=N; the         }  *     } $cout<<pr<<Endl;Panax Notoginseng     return 0; -}

1.3.1 Mixing Milk