CF870F Paths

You are given a positive integer $ n $ . Let's build a graph on vertices $ 1,2,...,n $ in such a way that there is an edge between vertices $ u $ and $ v $ if and only if . Let $ d(u,v) $ be the shortest distance between $ u $ and $ v $ , or $ 0 $ if there is no path between them. Compute the sum of values $ d(u,v) $ over all $ 1

Single integer $ n $ ( $ 1

Print the sum of $ d(u,v) $ over all $ 1

All shortest paths in the first example: -  -  -  -  -  -  There are no paths between other pairs of vertices. The total distance is $ 2+1+1+2+1+1=8 $ .