using namespace std;
struct Node{
	int time,number;
}a[102];
int m,n;
bool cmp(Node a,Node b){
	if(a.time!=b.time){
		return a.time<b.time;
	}
	return a.number>b.number;
}
int ans;
int main()
{
    cin>>m>>n;
    for(int i=0;i<n;i++){
    	cin>>a[i].time>>a[i].number;
	}
	sort(a,a+n,cmp);
	for(int i=0;i<n;i++){
		if(a[i].time<=m){
			ans+=a[i].number;
			m-=a[i].time;
		}
	}
	cout<<ans;
    return 0;
}