void dfs(int v) {
    visited[v] = true;
    sizes[v] = 1;
    for (int i = 0; i < ways[v].size(); i++) {
        if (!visited[ways[v][i]]) {
            dfs(ways[v][i]);
            sizes[v] += sizes[ways[v][i]];
        }
    }
}

int find_center(int v, int n, int p) {
    for (int i = 0; i < ways[v].size(); i++) {
        if (!visited[ways[v][i]] && sizes[ways[v][i]] > n / 2 && ways[v][i] != p) {
            return find_center(ways[v][i], n, v);
        }
    }
    return v;
}

int build(int v, int n, int last) {
    int center = find_center(v, n, v);
    visited[center] = true;
    p[center] = last;
    for (int i = 0; i < ways[center].size(); i++) {
        if (!visited[ways[center][i]]) {
            int z = build(ways[center][i], n / 2, center);
        }
    }
    return center;
}