B'There are n departments in the mall, each of which has exactly two stores. For convenience, we number the departments with integers from 1 to n . It is known that gifts in the first store of the i department cost a_i rubles, and in the second store of the i department -- b_i rubles. Entering the mall, Sasha will visit each of the n departments of the mall, and in each department, he will enter exactly one store. When Sasha gets into the i -th department, he will perform exactly one of two actions: Sasha is going to buy at least one gift for each friend. Moreover, he wants to pick up gifts in such a way that the price difference of the most expensive gifts bought for friends is as small as possible so that no one is offended. More formally: let m_1 be the maximum price of a gift bought to the first friend, and m_2 be the maximum price of a gift bought to the second friend. Sasha wants to choose gifts in such a way as to minimize the value of lvert m_1 - m_2 rvert . Each test contains multiple test cases. The first line contains the number of test cases t ( 1 <= t <= 1 ,000 ). The description of the test cases follows. The first line of each test case contains a single integer n ( 2 <= n <= 500 ,000 ) -- the number of departments in the mall. Each of the following n lines of each test case contains two integers a_i and b_i ( 0 <= a_i, b_i <= 10^9 ) -- the prices of gifts in the first and second store of the i department, respectively. It is guaranteed that the sum of n over all test cases does not exceed 500 ,000 . Print one integer -- the minimum price difference of the most expensive gifts bought to friends. In the first test case, Sasha has two possible options: buy a gift for the first friend in the first department, and the second friend -- in the second department, or vice versa. In the first case, '...