program fibo3;

function fib( cislo: integer ): double;
var
	i: integer;
	levy, pravy, tento: double;
begin
	if cislo < 2 then begin
		fib := cislo;
		exit;
	end;
	levy := 0;
	pravy := 1;
	for i := 2 to cislo do begin
		tento := levy + pravy;
		levy := pravy;
		pravy := tento;
	end;
	fib := pravy;
end;

begin
	writeln( fib( 4 ) );
	writeln( fib( 5 ) );
	writeln( fib( 6 ) );
	writeln( fib( 5000 ) );
end.