Description：

Solution：

Code：

#include<algorithm>

#include<iostream>

#include<cstdlib>

#include<cstdio>

#include<cmath>

#include<queue>

#include<cstring>

using namespace std;

int n,m;

#define MAXN 500010

struct edge

{

	int to,nxt;

}e[MAXN << 1];

int edgenum = 0;

int lin[MAXN] = {0};

void add(int a,int b)

{

	++edgenum;e[edgenum].to = b;e[edgenum].nxt = lin[a];lin[a] = edgenum;

	++edgenum;e[edgenum].to = a;e[edgenum].nxt = lin[b];lin[b] = edgenum;

	return;

}

int s[MAXN];

int f[MAXN][20];

int dep[MAXN];

bool v[MAXN];

int fa[MAXN];

int find(int x){return (fa[x] == x ? x : fa[x] = find(fa[x]));}

int LCA(int a,int b)

{

	if(dep[a] < dep[b])swap(a,b);

	for(int i = 19;i >= 0;--i)

		if(dep[f[a][i]] >= dep[b])

			a = f[a][i];

	if(a == b)return a;

	for(int i = 19;i >= 0;--i)

		if(f[a][i] != f[b][i])

			a = f[a][i],b = f[b][i];

	a = f[a][0];b = f[b][0];

	return a;

}

int main()

{

	freopen("train.in","r",stdin);

	freopen("train.out","w",stdout);

	scanf("%d%d%d",&n,&m,&s[0]);

	int a,b;

	for(int i = 1;i < n;++i)

	{

		scanf("%d%d",&a,&b);

		add(a,b);

	}

	for(int i = 1;i <= n;++i)fa[i] = i;

	queue<int> q;

	q.push(1);dep[1] = 1;

	while(!q.empty())

	{

		int k = q.front();q.pop();

		v[k] = true;

		for(int i = lin[k];i != 0;i = e[i].nxt)

		{

			if(v[e[i].to])continue;

			f[e[i].to][0] = k;

			dep[e[i].to] = dep[k] + 1;

			q.push(e[i].to);

		}

	}

	for(int k = 1;k <= 19;++k)

		for(int i = 1;i <= n;++i)

			f[i][k] = f[f[i][k - 1]][k - 1];

	long long res = 0;

	int k = s[0];

	int cur = s[0];

	for(int i = 1;i <= m;++i)

	{

		scanf("%d",&s[i]);

		if(find(s[i]) == k)continue;

		a = s[i];b = cur;

		int lca = LCA(a,b);

		res += dep[a] + dep[b] - 2 * dep[LCA(a,b)];

		while(true)

		{

			if(dep[find(a)] > dep[lca])

			{

				fa[find(a)] = f[find(a)][0];

				a = find(a);

			}

			else break;

		}

		while(true)

		{

			if(dep[find(b)] > dep[lca])

			{

				fa[find(b)] = f[find(b)][0];

				b = find(b);

			}

			else break;

		}

		k = find(a);

		cur = s[i];

	}

	cout << res << endl;

	fclose(stdin);

	fclose(stdout);

	return 0;

}