#include<bits/stdc++.h>
using namespace std;
int ans,t,m;
struct cy{
	int time,money;
	double xjb;
}a[110];
bool cmp(cy x,cy y){
	return x.xjb>=y.xjb;
}
int main(){
	cin>>t>>m;
	for(int i=1;i<=m;i++){
		cin>>a[i].time>>a[i].money;
		a[i].xjb=a[i].money/a[i].time;
	}
	sort(a+1,a+m+1,cmp);
	int i=0;
	while(t>0&&i<=m){
		if(a[++i].time<=t)ans+=a[i].money,t-=a[i].time;
	}
	cout<<ans;
	return 0;
}