Untitled

#include <bits/stdc++.h>
using namespace std;
#define ll long long
int tt, tc;

void solve() {
	int n;
    cin >> n;
    vector<int> col(n);
    for (int& u : col) {
        cin >> u;
        --u;
    }
    vector<vector<int>> g(n);
    for (int i = 0; i < n - 1; i++) {
        int u, v;
        cin >> u >> v;
        --u, --v;
        g[u].push_back(v);
        g[v].push_back(u);
    }

    vector<int> d(n), p(n, -1);
    vector<int> bfs = {0};
    for (int i = 0; i < n; i++) {
        int v = bfs[i];
        for (int u : g[v]) if (u != p[v]) {
            p[u] = v;
            d[u] = d[v] + 1;
            bfs.push_back(u);
        }
    }

    vector<vector<int>> of_color(n);
    for (int i = 0; i < n; i++) {
        of_color[col[i]].push_back(d[i] & 1);
    }

    for (int c = 0; c < n; c++) {
        auto& V = of_color[c];
        if (V.empty()) continue;
        for (int i = 1; i < (int)V.size(); i++) if (V[i] != V[i - 1]) {
            cout << -1 << "\n";
            return;
        }
    }

    int occ = 0;
    for (int u : d) occ += (u & 1);
    cout << min(occ, n - occ) << "\n";
}

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	tt = 1, tc = 1;
	// cin >> tt;
	while (tt--) {
		solve();
		tc++;
	}
}