Minimum Cost to Convert All 1s to 0s with Fixed-Length Window Operations

You are given a binary array product of length n and a positive integer k. You want to convert all 1s to 0s with minimum total cost. You may repeat the following operation: Choose a subarray [l, r] of length exactly k (so r - l + 1 = k). The cost of this operation is sum(product[l..r]). Then choose an index p in [l, r] such that product[p] = 1 and set it to 0. When there are no 1s left, the process ends. Return the minimum possible total cost. Suggested Input Line 1: n Line 2: product (n integers 0/1) Line 3: k Output Minimum total cost. Constraints (typical) 1 <= n <= 2e5, 1 <= k <= n, product[i] in {0,1} Example Input 5 1 0 1 1 0 3 Output (unknown)