City Block Partition

Problem Statement

In the city of Gridopolis , the city is arranged in a block formation with 2 parallel streets and n intersections (blocks) along each street. Some blocks are open and accessible (free) while others are closed for construction (blocked). A block is accessible if it has a free passage on at least one of the streets. Residents of Gridopolis want to ensure that their neighborhoods remain connected. Two blocks are part of the same neighborhood if they are accessible and can be reached through adjacent blocks (either horizontally or vertically). Your task is to identify the critical blocks in the city grid: the block that, if closed for construction, would divide the city into exactly 3 separate neighborhoods . Additional Constraints: Initially, there is at most 1 connected neighborhood in the city grid. Input The first line contains a single integer n (1 ≤ n ≤ 200,000) — the number of blocks along each of the two streets. The next two lines represent the city grid: Each line contains a stri