Minimum Operations

Suppose you have an array $B \ (0 \leq B_i \leq 10^9)$ of length $M$, and a positive integer $K \ (1 \leq K \lt M)$. You are allowed to do the following operation on $B$: - Select $x$ indices $i_1, i_2, \ldots, i_x \ (1 \leq i_j \leq M)$, such that $(i_{j + 1} - i_j) \geq K$ for all $1 \leq j \lt x$; - Subtract $1$ to $B_{i_j}$ for all $1 \leq j \leq x$. For the array $B$ and integer $K$, let