Školjka

%V0 Let $n$ and $k$ be positive integers such that $\frac{1}{2} n < k \leq \frac{2}{3} n.$ Find the least number $m$ for which it is possible to place $m$ pawns on $m$ squares of an $n \times n$ chessboard so that no column or row contains a block of $k$ adjacent unoccupied squares.