program slo; // listopad 2016, runda próbna
type  Ti=longint;  Tq=qword;
 Tlitera= array['a'..'c'] of char;
var n,na,i:Ti;  k,ka:Tq;  wa:char; //wa:wezeł aktualny
  sq2: array[1..1000000] of Tq;//potęgi 2-ki
  sucL: Tlitera = ('b','a','a');
  sucP: Tlitera = ('c','c','b');

begin
  readln(n,k); na:=n; ka:=k;
  sq2[1]:=2;
  for i:=2 to 60 do sq2[i]:=sq2[i-1]*2;
  for i:= 61 to n do sq2[i]:=sq2[i-1]+2;
//  writeln(sq2[60]); writeln(sq2[60]*2);
  if k>3*(sq2[n]-1) then  begin writeln('NIE'); exit end;
  if k<sq2[n] then wa:='a' else if k<2*sq2[n]-1 then wa:='b' else wa:='c';
  case wa of 'b': ka-=sq2[na]-1; 'c': ka-=2*(sq2[na]-1) end; //case
  write(wa);

  while ka>1 do
  begin
    if ka<=sq2[na-1] then wa:=sucL[wa]
    else begin wa:=sucP[wa]; ka:=ka-sq2[na-1]+1 end;
    ka-=1; na-=1;
    write(wa);
  end; //while
  writeln;
end.