Part of course:
Free ticket (INOI 2014: India)
Problem in short: Given a weighted undirected graph with C nodes and F edges, find the distance between the nodes that are furthest away from each other. Here, distance = shortest-path distance. C <= 250, F <= 25,000.
Indian National Olympiad in Informatics (INOI) is round 2 out of 3 (i.e. intermediate) for selection into Indian IOI team.