N cities are required to connect with each other by a new transportation system. After several rounds of bidding, we have selected M constructions companies and
decided which section is assigned to which company, the associated cost and the direction of each road.
Due to the insufficiency of national fiscal revenue and special taxation system (the tax paid by each company pays is a fixed amount and tax payment occurs at the
beginning of the construction of the project) The government wishes to complete the project in several years and collects as much tax as possible to support the public
expense
For the restrictions of construction and engineering techniques, if a company is required to start the construction, then itself and its associated companies have to
complete all the tasks they commit (if company A constructs a road
from city 1 to city 2, company B constructs a road from city 2 to city 3, company C constructs a road from city 1 to city 3, we call
companies A and B are associated and other company pairs have no such relationship, pay attention, in this example and a are not associated, in other words,’
associated' is a directed relationship).
Now the question is what the maximum income the government can obtain in the first year is?