#include<bits/stdc++.h> using namespace std; struct homo{ int q,bl,dq; }aaa[114]; int f[91981]; int n,m; int main(){ cin>>n>>m; for(int i=1;i<=m;i++){ cin>>aaa[i].q>>aaa[i].bl; aaa[i].dq=aaa[i].q*aaa[i].bl; for(int j=n;j>=aaa[i].q;j--){ f[j]=max(f[j],f[j-aaa[i].q]+aaa[i].dq); } } cout<<f[n]<<endl; return 0; }