暴力60...

var a,b,c,i,n:qword;
begin
  read(n);
  if n<3 then
  begin
    writeln(n);
    halt;
  end;
  a:=1;
  b:=2;
  for i:=3 to n do
  begin
    c:=a+b;
    a:=b;
    b:=c;
  end;
  writeln(c);
end.