program   economie;
type   vector=array[1..50000] of byte;
       vectori=array[1..50000] of longint;
var       n,p,i,j:longint;
          v:vector;
          baza:vectori;
          f:text;




begin
assign(f,'economie.in'); reset(f); readln(f,n);fillchar(v,sizeof(v),0);
for i:=1 to n do
       begin
       read(f,p);
       v[p]:=1;
       end;
close(f);
i:=1;p:=0;
while i<=50000 do
begin
while (i<=50000) and (v[i]<>1) do inc(i);
if i<=50000 then begin
inc(p);
baza[p]:=i; v[i]:=2 ;n:=1;
while n<=50000-i do
        begin
        if v[n]=2 then v[n+i]:=2;
        n:=n+1;
       { if n+i>50000 then begin writeln(p,' ',baza[p]);readln;end;}
        end;
i:=i+1;  end;
end;
assign(f,'economie.out'); rewrite(f); writeln(f,p);
for i:=1 to p do writeln(f,baza[i]);
close(f);
















end.