#include <iostream>
#include <algorithm>
using namespace std;
const int N(30009);
int f[N]={0};
int main()
{
	int m,n,v,p;
	cin>>m>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>v>>p;
		for(int j=m;j>=v;j--)
			f[j]=max(f[j],f[j-v]+v*p);
	}
	cout<<f[m]<<endl;
	return 0;
}
/**************************************************************
	Problem: 2261
	User: admin
	Language: C++
	Result: Accepted
	Time:45 ms
	Memory:2192 kb
****************************************************************/