program bing;
var
 f1,f2:text;
 t,m,v,v0:integer;
 a:array[1..100,1..2]of integer;
 b:array[1..100] of boolean;
procedure init;
var i,j:integer;
begin
 assign(f1,'medic.in');reset(f1);
 assign(f2,'medic.out');rewrite(f2);
 readln(f1,t,m);
 for i:=1 to m do begin
  b[i]:=true;
  for j:=1to 2 do read(f1,a[i,j]); end;
 v:=0;v0:=0;
end;
procedure s(x:integer);
var i:integer;
begin
 for i:=1 to m do
  if (b[i]=true)and(a[i,1]<=x) then
  begin
   v:=v+a[i,2]; x:=x-a[i,1];b[i]:=false;
   if x=0 then
   begin
   if v>v0 then v0:=v;end
   else s(x);
   x:=x+a[i,1];
   v:=v-a[i,2];
   b[i]:=true;
  end
  else  if v>v0 then v0:=v;
end;
begin
 init;
 s(t);
 write(f2,v0);
 close(f1);close(f2);
end.