11.14

#include <iostream>
#include <vector>
#include <queue>
using namespace std;

int main() {
    int n, k;
    cin >> n >> k;

    vector<vector<int>> tree(n);
    for (int i = 0; i < n - 1; ++i) {
        int p, c;
        cin >> p >> c;
        tree[p].push_back(c);
        tree[c].push_back(p); 
    }

    vector<int> node_value(n);
    int target_node = -1;

    for (int i = 0; i < n; ++i) {
        cin >> node_value[i];
        if (node_value[i] == k) {
            target_node = i;
        }
    }

    vector<int> depth(n, -1);
    queue<int> q;
    q.push(0);
    depth[0] = 0;

    while (!q.empty()) {
        int node = q.front();
        q.pop();

        for (int child : tree[node]) {
            if (depth[child] == -1) { 
                depth[child] = depth[node] + 1;
                q.push(child);
            }
        }
    }

    cout << depth[target_node] << endl;
    return 0;
}