program tz;
type score=array[1..100,1..2] of integer;
var a:score;p,s,t,m,i,j:integer;biaozhi:boolean;f1,f2:text;
begin
  assign(f1,'medic.in');
  assign(f2,'medic.out');
  reset(f1);rewrite(f2);
  readln(f1,t,m);
  for i:=1 to m do
    begin
      for j:=1 to 2 do
        read(f1,a[i,j]);
    end;
  s:=0;p:=0;
  for i:=1 to m do
    begin
    if a[i,1]<t then p:=p+a[i,1];
    if (p<>0)and(p<=t) then s:=s+a[i,2];
    end;
  writeln(f2,s);
  close(f1);
  close(f2);
end.