<image>One day, the teacher assigned an extracurricular task involving a square grid composed of $$m \times n (m \times n > 1)$$ small squares. The goal was to study the number of small squares $$f$$ that a diagonal line passes through when $$m$$ and $$n$$ are coprime (no common factors other than 1). As shown in the figure, Xiao Liang selected a pattern of 5 to observe, from which the relationship between the number of small squares $$f$$ and $$m$$, $$n$$ can be deduced as ______. 
