#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;
float a[100],b[100];
struct wu{
	int xu;
	float z;
};
bool cm(wu a,wu b)
{
	return a.z>b.z;
}
int main()
{
	int n,m;
	long long sum=0;
	wu wu[30];
	cin>>n>>m;
	for(int i=0;i<m;i++)
	{
		cin>>a[i]>>b[i];
		wu[i].z=b[i]/a[i];
		wu[i].xu=i;
	}
	sort(wu,wu+m,cm);
	for(int i=0;i<m;i++)
	{
		if(n-a[wu[i].xu]>=0)
		{
			sum+=wu[i].z*a[wu[i].xu]*a[wu[i].xu];
			n-=a[wu[i].xu];
		}
	}
	cout<<sum;
	return 0;
 }