#include <iostream>

#include <string.h>

using namespace std;

#include <set>

int total[+];

int v[];

int p[];

int main()

{

    int money,n;

    while(cin>>money>>n)

    {

        memset(total,,sizeof(total));

        for(int i=;i<n;i++)

        {

         cin>>v[i]>>p[i];

        }

       for(int j=;j<n;j++)

       {

            for(int i=money;i-v[j]>=;i--)

        {

               if(total[i-v[j]]+v[j]*p[j]>total[i])

               {

                   total[i]=total[i-v[j]]+v[j]*p[j];

               }

        }

       }

       cout<<total[money]<<endl;

    }

    return ;

}