#include<iostream>  
#include<cstdio>
#include<cmath>
#include<cctype>  
#include<cstring>  
#include<algorithm>  
using namespace std; 
int m,n;
int f[30001]={0},w[26]={0},a[26]={0};
int max(int a,int b)
{
    if(a>b)
	{
	    return a;
	}
	else
	{
	    return b;
	}
}
int main()
{ 
    freopen("happy.in","r",stdin);        
    freopen("happy.out","w",stdout);      
	cin>>m>>n;
	for(int i=1;i<=n;i++)
	{
	    cin>>w[i]>>a[i];
	}
	for(int i=1;i<=n;i++)
	{
	    for(int j=m;j>=w[i];j--)
		{
		    f[j]=max(f[j-w[i]]+w[i]*a[i],f[j]);
		}
	}
	cout<<f[m];
    return 0;  
}