7046번 - Journey 다국어

문제

There are n cities in Byteland (numbered from 1 to n), connected by bidirectional roads. The king of Byteland is not very generous, so there are only n-1 roads, but they connect the cities in such a way that it is possible to travel from each city to any other city.

One day, a traveller Byterider arrived in the city number k. He was planning to make a journey starting in the city k and visiting on his way cities m₁ , m₂ , ..., m_j (not necessarily in this order) - the numbers m i are all different and they are also different from k. Byterider - like every traveller - has only a limited amount of money, so he would like to visit all the cities that he has planned to visit using the shortest possible path (starting in the city k). A path is one road or a sequence of roads, where every next road begins in the city where the previous one ends. Help Byterider to determine the length of the shortest path for his journey.

Write a program which

• reads from the standard input:
  • the description of the roads connecting the cities of Byteland,
  • the number of the city where Byterider arrived,
  • a list of cities which Byterider would like to visit.
• determines the minimum length of Byterider's journey,
• writes the result to the standard output

입력

The first line of the standard input contains two integers n and k separated by a single space (2 ≤ n ≤ 50000, 1 ≤ k ≤ n), n is the number of cities in Byteland and k is the number of the first city on Byterider's path. Each of the following n-1 lines contains the description of one road in Byteland. Line (i + 1) (for 1 ≤ i ≤ n-1) contains three integers a_i, b_i and d_i separated by single spaces (1 ≤ ai, b_i ≤ n, 1 ≤ d_i ≤ 1000), a_i and b_i are the cities connected by the road, and d_i is the length of the road. Line (n + 1) contains one integer j - the number of cities which Byterider would like to visit (1 ≤ j ≤ n-1). The next line contains j different integers m_i separated by single spaces - the numbers of the cities that Byterider would like to visit (1 ≤ m_i ≤ n, m_i ≠ k).

출력

The first and only line of the standard output should contain exactly one integer: the length of the shortest path for Byterider's journey.

제한

힌트