CodeForces 16B Burglar and Matches(贪心)

B. Burglar and Matches

time limit per test

0.5 second

memory limit per test

64 megabytes

input

standard input

output

standard output

A burglar got into a matches warehouse and wants to steal as many matches as possible. In the warehouse there are mcontainers, in the i-th container there are ai matchboxes, and each matchbox contains bi matches. All the matchboxes are of the same size. The burglar's rucksack can hold n matchboxes exactly. Your task is to find out the maximum amount of matches that a burglar can carry away. He has no time to rearrange matches in the matchboxes, that's why he just chooses not more than n matchboxes so that the total amount of matches in them is maximal.

Input

The first line of the input contains integer n (1 ≤ n ≤ 2·108) and integer m (1 ≤ m ≤ 20). The i + 1-th line contains a pair of numbers ai and bi (1 ≤ ai ≤ 108, 1 ≤ bi ≤ 10). All the input numbers are integer.

Output

Output the only number — answer to the problem.

Sample test(s)

input

7 35 102 53 6

output

62

input

3 31 32 23 1

output

7

很水的贪心  直接每次选装的多的盒子  n减去盒子数就行了

#include<cstdio>#include<cstring>#include<algorithm>using namespace std;const int M = 25;int a[M], b[M], c[M], n, m, ans;bool cmp (int i, int j){    return b[i] > b[j];}int main(){    scanf ("%d%d", &n, &m);    for (int i = 1; i <= m; ++i)    {        c[i] = i;        scanf ("%d%d", &a[i], &b[i]);    }    sort (c + 1, c + m + 1, cmp);    ans = 0;    for (int i = 1; i <= m; ++i)    {        if (n >= a[c[i]])        {            n -= a[c[i]];            ans += a[c[i]] * b[c[i]];        }        else        {            ans += n * b[c[i]];            break;        }    }    printf ("%d\n", ans);    return 0;}