#include
#include
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
scanf("%d%d", &buf[i].price, &buf[i].volume);
sort(buf, buf+n);
ids = 0;
ans = 0;
while(v>0 && ids
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;
class jewelry {
public int price;
public int volume;
boolean compareto (jewelry A) {
return this.price > A.price;
}
static jewelry[] buf = new jewelry[101];
void main() {
int v, n, i, ans, ids;
Scanner in = new Scanner(System.in);
while(in.hasNextInt()) {
v = in.nextInt();
n = in.nextInt();
for(i=0; i<n; i++)
{
buf[i] = new jewelry();
buf[i].price= in.nextInt();
buf[i].volume = in.nextInt();
}
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++;
}
System.out.println(ans);
}
return 0;
}