Statement

In Italy there are N cities numbered from 0 to N-1. Luca lives in city S, but for the holidays he decided to go visit city E. Being just a student he doesn't want to spend a fortune in plane tickets, so he decided to have a nice bus trip! Luca used a Bash script to download the complete schedules of all the bus companies in the country. He collected M bus routes, and for each of those he has collected the following four details: (1) the starting city; (2) the time of bus departure; (3) the arrival city; (4) the time of bus arrival. Assuming that Luca is located in the city S at time t = 0, help him compute the earliest possible time he can reach the city E to enjoy his holiday, by using as many buses as needed.