274B - Zero Tree

using namespace std;
using ll = long long;
using vi = vector<int>;
int const NMAX = 1e5 + 11;
int n;
ll val[NMAX];
vi g[NMAX];
array<ll, 2> dfs(int u, int p)
{
    array<ll, 2> ans = {0, 0};
    for (auto v : g[u])
    {
        if (v == p)
            continue;
        auto cur = dfs(v, u);
        ans = {max(ans[0], cur[0]), max(ans[1], cur[1])};
    }
    val[u] += ans[0] - ans[1];
    ans[val[u] >= 0] += abs(val[u]);
    val[u] = 0;
    return ans;
}
int main(void)
{
    int u, v;
    cin >> n;
    for (int i = 0; i < n - 1; ++i)
    {
        cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    for (int i = 1; i <= n; ++i)
        cin >> val[i];
    auto ans = dfs(1, -1);
    cout << accumulate(ans.begin(), ans.end(), 0LL) << endl;
    return 0;
}