#!/usr/bin/env pypy3

from collections import deque

INF = 2 ** 60


def get_dist(s, g):
    if s == g:
        return 0
    dist = [INF for _ in edge]
    dist[s] = 0
    q = deque()
    q.append(s)
    while True:
        p = q.popleft()
        for c, t in edge[p]:
            if t == g:
                return dist[p] + c
            if dist[t] == INF:
                dist[t] = dist[p] + c
                q.append(t)


def calc(s, dp, l, ds):
    res = [i for i in dp]
    dist = [INF for _ in dp]
    vis = [False for _ in dp]
    st = deque()
    st.append(s)
    dist[s] = l

    while st:
        p = st[-1]
        if vis[p]:
            st.pop()
            for c, t in edge[p]:
                if dist[p] < dist[t]:
                    res[p] = min(res[p], res[t])
        else:
            vis[p] = True
            res[p] += min(dist[p], ds)
            for c, t in edge[p]:
                if dist[t] == INF:
                    dist[t] = dist[p] + c
                    st.append(t)

    return res


n, q, c = map(int, input().split())

edge = [[] for _ in range(n)]
for _ in range(n - 1):
    u, v, l = map(int, input().split())
    u -= 1
    v -= 1
    edge[u].append((l, v))
    edge[v].append((l, u))

x = list(map(lambda y: int(y) - 1, input().split()))
dp = [INF for _ in range(n)]
dp[x[0]] = 0
for prev, y in zip(x, x[1:]):
    d = get_dist(prev, y)
    dp = calc(y, dp, c, d)

print(min(dp))