CodeForces - 1060E Sergey and Subway(树上任意两点之间的距离和)
SergeyandSubwaySergeySemyonovichisamayorofacountycityNandheusedtospendhisdaysandnightsinthoughtsoffurtherimprovementsofNkers'lives.Unfortunatelyforhim,anythingandeverythinghasbeendonealready,andtherea