#include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>

using namespace std;

#define MAX 20005

int n, m;
int tin[MAX], tout[MAX];
int up[MAX][25];
int timer;
int l;

void dfs(int v, int p, vector<vector<int> > &graph){
    timer++;
    tin[v] = timer;
    up[v][0] = p;
    for(int i = 0; i <= l; i++){
        up[v][i] = up[up[v][i-1]][i-1];
    }
    for(int u: graph[v]){
        if(u!=p) dfs(u, v, graph);
    }
    timer++;
    tout[v] = timer;
}

bool is_ancestor(int u, int v){
    return tin[u] <= tin[v] && tout[u] >= tout[v];
}

int lca(int u, int v){
    if(is_ancestor(u, v)){
        return u;
    }
    if(is_ancestor(v, u)) return v;
    for(int i = l; i>=0; i--){
        if(!is_ancestor(up[u][i], v)) u = up[u][i];
    }

    return u;
}

int main(){
    cin >> n >> m;
    vector<vector<int> > graph(n+1);
    for(int i = 1; i <= n-1; i++){
        int x, y;
        cin >> x >> y;
        x--, y--;
        graph[x].push_back(y);
    }
    for(auto v: graph){
        sort(v.begin(), v.end());
    }
    l = ceil(log2(n));
    timer = 1;
    dfs(0, 0, graph);

    int res = 1;
    vector<int> ppl;
    int p;
    for(int i = 0; i < m; i++){
        cin >> p;
        p--;
        ppl.push_back(p);
    }

    for(int i = 0; i < m-1; i++){
        int u = ppl[i], v = ppl[i+1];
        if(is_ancestor(u, v) || is_ancestor(v, u)){res++;continue;}
        int up_u = lca(u, v), up_v = lca(v, u);
        if(up_u > up_v) break;
        res++;
    }

    cout << res << endl;
}