杭电acm2111

贪心

#include <stdio.h>
#include <algorithm>

using namespace std;

struct jewelry {
	int price;
	int volume;
	
	bool operator < (const jewelry &A) const {
		return price > A.price;
	}
	
}buf[101];

int main() {
	
	int v, n, i, ans, ids;
	while(~scanf("%d", &v) && v) {
		scanf("%d", &n);
		for(i=0; i<n; i++)
			scanf("%d%d", &buf[i].price, &buf[i].volume);
		sort(buf, buf+n);
		
		ids = 0;
		ans = 0;
		while(v>0 && ids<n) {
			
			if(v>=buf[ids].volume) {
				v -= buf[ids].volume;
				ans += buf[ids].price * buf[ids].volume;
			} else {
				ans += v * buf[ids].price;
				v = 0;
			}
			ids ++;
		}
		
		printf("%d\n", ans);
	}
	
	return 0;
}