MathDB

Let

A

and

B

two countries which inlude exactly

2011

cities.There is exactly one flight from a city of

A

to a city of

B

and there is no domestic flights (flights are bi-directional).For every city

X

(doesn't matter from

A

or from

B

), there exist at most

19

different airline such that airline have a flight from

X

to the another city.For an integer

k

, (it doesn't matter how flights arranged ) we can say that there exists at least

k

cities such that it is possible to trip from one of these

k

cities to another with same airline.So find the maximum value of

k

Problem Statement