I'm trying to solve 720B — Cactusophobia from Russian Code Cup 2016 Final. I read the editorial and understood the flow solution for this problem. So I find some implementation for this problem. I read dreamoon_love_AA's solution (20732895), which used Dinic flow finding algorithm and run in 373ms. But, since Dinic algorithm run in O(n²m), and the graph can have up to 30000 vertices and edges, how could this run in time? Can someone enlighten me about this? Thanks in advance.