#include <bits/stdc++.h>
int input(){
  int a;
  cin >> a;
  return a;
}
struct Farmer{
	int cost;
	int many;
}a[1000000];
bool cmp (Farmer a,Farmer b){
	if (a.cost != b.cost) return a.cost < b.cost;
	return a.many > b.many;
}
int main(){
	int n = input(),m = input();
	for (int i = 1;i <= m;i ++) a[i].cost = input(),a[i].many = input();
	sort (a + 1,a + n + 1,cmp);
	int i = 1,ans = 0;
	while (n){
		if (a[i].many){
			a[i].many --;
			ans += a[i].cost;
			n --;
		}
		else i ++;
	}
    cout<<ans;
	return 0;
}