D. Exploration plantime limit per test2 secondsmemory limit per test256 megabytesinputstandard inputoutputstandard outputThe competitors of Bubble Cup X gathered after the competition and discussed what is the best way to get to know the host country and its cities.After exploring the map of Serbia for a while, the competitors came up with the following facts: the country has V cities which are indexed with numbers from 1 to V, and there are E bi-directional roads that connect the cites. Each road has a weight (the time needed to cross that road). There are N teams at the Bubble Cup and the competitors came up with the following plan: each of the N teams will start their journey in one of the V cities, and some of the teams share the starting position.They want to find the shortest time T, such that every team can move in these T minutes, and the number of different cities they end up in is at least K (because they will only get to know the cities they end up in). A team doesn't have to be on the move all the time, if they like it in a particular city, they can stay there and wait for the time to pass.Please help the competitors to determine the shortest time T so it's possible for them to end up in at least K different cities or print -1 if that is impossible no matter how they move.Note that there can exist multiple roads between some cities.InputThe first line contains four integers: V, E, N and K (1 ≤  V  ≤  600,  1  ≤  E  ≤  20000,  1  ≤  N  ≤  min(V, 200),  1  ≤  K  ≤  N), number of cities, number of roads, number of teams and the smallest number of different cities they need to end up in, respectively.The second line contains N integers, the cities where the teams start their journey.Next E lines contain information about the roads in following format: Ai Bi Ti (1 ≤ Ai, Bi ≤ V,  1 ≤ Ti ≤ 10000), which means that there is a road connecting cities Ai and Bi, and you need Ti minutes to cross that road.OutputOutput a single integer that represents the minimal time the teams can move for, such that they end up in at least K different cities or output -1 if there is no solution.If the solution exists, result will be no greater than 1731311.ExampleInput6 7 5 45 5 2 2 51 3 31 5 21 6 52 5 42 6 73 4 113 5 3Output3NoteThree teams start from city 5, and two teams start from city 2. If they agree to move for 3 minutes, one possible situation would be the following: Two teams in city 2, one team in city 5, one team in city 3 , and one team in city 1. And we see that there are four different cities the teams end their journey at.
Input6 7 5 45 5 2 2 51 3 31 5 21 6 52 5 42 6 73 4 113 5 3
Output3
['binary search', 'flows', 'graph matchings', 'shortest paths', '*2100']