#include <bits/stdc++.h>
using namespace std;
struct E{
	int shi;
	int jia;
	double p;
}arr[105];

bool C(E a,E b){
	if(a.p>b.p) return 1;
	else return 0;
}

int main(){
	int t,m,s,kkk=0,jk=0;
	cin>>t>>m;
	for(int i=0;i<m;i++){
		cin>>arr[i].shi>>arr[i].jia;
		arr[i].p=(double)arr[i].shi/arr[i].jia;
	}
	sort(arr,arr+m,C);
	for(int i=0;;i++){
		if(t>=arr[jk].shi){
//			cout<<arr[i].shi<<" "<<arr[i].jia<<" "<<arr[i].p<<" "<<kkk<<" "<<t<<endl;
			t=t-arr[jk].shi;
			kkk+=arr[jk].jia;
			jk++;
		}else{
			jk++;
		} 
		if(jk>m){
			break;
		}
	}
	cout<<kkk;
}