#!/usr/bin/env pypy3

import sys
sys.setrecursionlimit(6000)

INF = 2 ** 60


def dfs_dist(p, par, g):
    if p == g:
        return 0
    for c, t in edge[p]:
        if t == par:
            continue
        d = c + dfs_dist(t, p, g)
        if d < INF:
            return d
    return INF


def dfs(p, par, l, ds):
    dp[p] += min(l, ds)
    for c, t in edge[p]:
        if t == par:
            continue
        dp[p] = min(dp[p], dfs(t, p, l + c, ds))
    return dp[p]


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 = dfs_dist(prev, -1, y)
    dfs(y, -1, c, d)

print(min(dp))