Now I get it, I was misinterpreting question all this time. Actually after finish of each round, lead is not the difference between points of that round. But the lead is difference between the points achieved through all rounds including current round - Lakpa Tashi Bhutia
Problem in short: There are N people, and person i takes a[i], b[i] and c[i] time to do task a, b, c respectively. Only one person can do task a at a given point of time, and each person must do tasks a, b, c in-order. In which order should the N people do task a, so as to minimize the time at which everyone is done with all of their tasks. N <= 2 * 10^5.
Indian National Olympiad in Informatics (INOI) is round 2 out of 3 (i.e. intermediate) for selection into Indian IOI team.