Problem 3.4 Prove that the sum of any n entries of the table $$\begin{array}{c@{\quad}c@{\quad}c@{\quad}c@{\quad}c}1 & \frac{1}{2} & \frac{1}{3} & \ldots & \frac{1}{n}\\[4pt]\frac{1}{2} & \frac{1}{3} & \frac{1}{4} & \ldots & \frac{1}{n+1}\\[4pt]\vdots & & & & \\[4pt]\frac{1}{n} & \frac{1}{n+1} & \frac{1}{n+2} & \ldots & \frac{1}{2n-1}\end{array}$$ situated in different rows and different columns is not less than 1.