// ---------- begin chmin, chmax ----------
trait ChangeMinMax {
    fn chmin(&mut self, x: Self) -> bool;
    fn chmax(&mut self, x: Self) -> bool;
}

impl<T: PartialOrd> ChangeMinMax for T {
    fn chmin(&mut self, x: Self) -> bool {
        *self > x && {
            *self = x;
            true
        }
    }
    fn chmax(&mut self, x: Self) -> bool {
        *self < x && {
            *self = x;
            true
        }
    }
}
// ---------- end chmin, chmax ----------
// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------

fn run() {
    input! {
        n: usize,
        q: usize,
        c: u64,
        e: [(usize1, usize1, u64); n - 1],
        x: [usize1; q],
    }
    let mut g = vec![vec![]; n];
    for &(a, b, c) in e.iter() {
        g[a].push((b, c));
        g[b].push((a, c));
    }
    let inf = std::u64::MAX / 3000;
    let dfs = |v: usize| -> (Vec<u64>, Vec<usize>, Vec<usize>) {
        let mut parent = vec![v; n];
        let mut dp = vec![inf; n];
        dp[v] = 0;
        let mut s = vec![v];
        for i in 0..n {
            let v = s[i];
            let d = dp[v];
            for &(u, c) in g[v].iter() {
                if dp[u].chmin(d + c) {
                    parent[u] = v;
                    s.push(u);
                }
            }
        }
        (dp, parent, s)
    };
    let mut dp = vec![inf; n];
    let mut pre = x[0];
    dp[pre] = 0;
    for &x in x[1..].iter() {
        let (depth, parent, topo) = dfs(x);
        let mut next = vec![inf; n];
        let mut warp = vec![inf; n];
        for &v in topo.iter().rev() {
            let d = dp[v];
            if v == pre {
                warp[v].chmin(d);
            } else {
                warp[v].chmin(d + c);
            }
            next[v].chmin(d + depth[pre]);
            next[v].chmin(warp[v] + depth[v]);
            let p = parent[v];
            let d = warp[v] + depth[v] - depth[p];
            warp[p].chmin(d);
        }
        dp = next;
        pre = x;
    }
    let ans = *dp.iter().min().unwrap();
    println!("{}", ans);
}

fn main() {
    run();
}