#include<bits/stdc++.h> 
using namespace std;
int n,times,sum;
struct tmd{
	int t;
	int v;
}a[9999999];
bool cmp(tmd x,tmd y){
	return x.v/x.t>y.v/y.t;
}
bool temp(tmd x,tmd y){
	return x.v<y.v;
}
int main(){
    cin>>times>>n;
    for(int i=1;i<=n;i++)cin>>a[i].t>>a[i].v;
    sort(a+1,a+1+n,temp);
	while(n>0&&a[n].t>times)n--; 
    sort(a+1,a+1+n,cmp);
    for(int i=1;i<=n&&times-a[i].t>=0;i++)times-=a[i].t,sum+=a[i].v;
    cout<<sum;
	return 0;
}