CREATE OR REPLACE FUNCTION int_to_roman(a INTEGER) RETURNS TEXT AS $$
BEGIN
    IF a > 3000 THEN
        RAISE EXCEPTION 'Number more 3000 --> %', a
              USING HINT = 'Please, use number lower 3000';
    ELSIF a < 0 THEN
        RAISE EXCEPTION 'Negative number --> %', a
              USING HINT = 'Please, use number more 0';
    ELSE
    RETURN to_char(a, 'FMRN');
    END IF;
END;
$$ LANGUAGE plpgsql;