#include<iostream>
#include<cstdio>
#define syy myson
using namespace std;
const int maxn=30010;
int n,m,w[30],p,d[30],f[maxn],i,j;
inline void input()
{
	scanf("%d%d",&n,&m);
	for(i=1;i<=m;i++)
	{
		scanf("%d%d",&w[i],&p);
		d[i]=w[i]*p;
	}
}
inline void work()
{
	for(i=1;i<=m;i++)
		for(j=n;j>=w[i];j--)
			if(f[j]<f[j-w[i]]+d[i])
				f[j]=f[j-w[i]]+d[i];
	printf("%d",f[n]);
}
int Main()
{
	freopen("happy.in","r",stdin);freopen("happy.out","w",stdout);
	input();
	work();
	return 0;
}
int main(){;};
int syy=Main();