分析：题不难，直接贴代码吧！

#include <iostream>
#include <algorithm>
#include <map>
#include <string>       #没有这行会报错
using namespace std;

struct treasure {
    int pi; //单价
    int pm; //体积
};

int cmp(struct treasure a, struct treasure b){
    return a.pi > b.pi;   //从大到小排序
}

int main() {
    int v,n;
    int count;
    int weight;
    struct treasure jiegou[100];

    while (cin >> v &&v){
        weight=v;
        count=0;
        cin >> n;

        for(int i=0;i<n;i++){
            cin >> jiegou[i].pi;
            cin >> jiegou[i].pm;
        }
        sort(jiegou,jiegou+n,cmp); //结构题排序

        for(int i=0;i<n;i++){
            if(weight >=jiegou[i].pm){
                count+=jiegou[i].pm*jiegou[i].pi;
                weight=weight-jiegou[i].pm;
                continue;
            } else{
                count+= (weight)*jiegou[i].pi;
                break;
            }
        }
        cout << count << endl;
    }

    return 0;
}