TREEREDBLACK

#include <bits/stdc++.h>
using namespace std;

const int INF = 1e9 + 7;
const int N = 105;

int n, m;
bool a[N];
int graph[N][N];

int d[N][N];

void Floyd() {
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= n; ++j)
            if (i != j)
                d[i][j] = graph[i][j];


    for (int k = 1; k <= n; ++k)
        for (int i = 1; i <= n; ++i)
            for (int j = 1; j <= n; ++j)
                d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
}

void solve() {
    cin >> n >> m;
    for (int i = 1; i <= n; ++i)
        cin >> a[i];

    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= n; ++j)
            graph[i][j] = INF;
    for (int i = 1; i < n; ++i) {
        int u, v; cin >> u >> v;
        graph[u][v] = graph[v][u] = 1;
    }

    Floyd();

    int ans = n;
    if (m == 2) {
        for (int i = 1; i <= n; ++i) {
            for (int j = 1; j <= n; ++j) {
                if (i != j && a[i] && a[j])
                    ans = min(ans, d[i][j]);
            }
        }

        cout << ans << '\n';
    } else {
        for (int i = 1; i <= n; ++i) {
            for (int j = 1; j <= n; ++j) {
                if (!a[i] || !a[j])
                    continue;

                int inc = 0, mx = d[i][j];
                for (int k = 1; k <= n; ++k) {
                    if (!a[k]) continue;

                    if (d[i][k] <= mx && d[k][j] <= mx) ++inc;
                }

                if (inc >= m)
                    ans = min(ans, mx);
            }
        }

        cout << ans << '\n';
    }


    return;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    solve();

    return 0;
}