#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define X first
#define Y second
#define ALL(v) v.begin(), v.end()
#define pb push_back
#define SZ(a) ((int)a.size())

const int N = 250005;

set<pair<ll, pll>> pr;
int org[N], tar[N], flag[N];

struct Cent_Dec {
    vector<pll> G[N];
    pll info[N];
    pll upinfo[N];
    int n, pa[N], layer[N], sz[N], done[N];
    ll dis[__lg(N) + 1][N];
    set<pll> st[2][N];
    void init(int _n) {
        n = _n, layer[0] = -1;
        fill_n(pa + 1, n, 0), fill_n(done + 1, n, 0);
        for (int i = 1; i <= n; ++i) G[i].clear();
    }
    void add_edge(int a, int b, int w) {
        G[a].pb(pll(b, w)), G[b].pb(pll(a, w));
    }
    void get_cent(int u, int f, int &mx, int &c, int num) {
        int mxsz = 0;
        sz[u] = 1;
        for (pll e : G[u])
            if (!done[e.X] && e.X != f) {
                get_cent(e.X, u, mx, c, num);
                sz[u] += sz[e.X], mxsz = max(mxsz, sz[e.X]);
            }
        if (mx > max(mxsz, num - sz[u]))
            mx = max(mxsz, num - sz[u]), c = u;
    }
    void dfs(int u, int f, ll d, int orgg) {
        dis[layer[orgg]][u] = d;
        if (flag[u] != -1) st[flag[u]][orgg].insert(pll(d, u));
        for (pll e : G[u])  
            if (!done[e.X] && e.X != f)
                dfs(e.X, u, d + e.Y, orgg);
    }
    int cut(int u, int f, int num) {
        int mx = 1e9, c = 0, lc;
        get_cent(u, f, mx, c, num);
        done[c] = 1, pa[c] = f, layer[c] = layer[f] + 1;
        for (pll e : G[c]) {
            if (!done[e.X]) {
                if (sz[e.X] > sz[c])
                    lc = cut(e.X, c, num - sz[c]);
                else lc = cut(e.X, c, sz[e.X]);
                upinfo[lc] = pll(), dfs(e.X, c, e.Y, c);
            }
        }
        if (flag[c] != -1) st[flag[c]][c].insert(pll(0, c));
        if (auto p = get_pr(c); p.X != -1) pr.insert(p);
        return done[c] = 0, c;
    }
    void build() { cut(1, 0, n); }
    pair<ll, pll> get_pr(int u) {
        if (st[0][u].empty() || st[1][u].empty()) return make_pair(-1, pll(-1, -1));
        //cerr << "get_pr " << u << ": " << st[0][u].begin()->X + st[1][u].begin()->X << " " << st[0][u].begin()->Y << " --> " << st[1][u].begin()->Y << "\n";
        return make_pair(st[0][u].begin()->X + st[1][u].begin()->X, pll(st[0][u].begin()->Y, st[1][u].begin()->Y));
    }
    void modify(int u) {
        assert(flag[u] != -1);
        for (int a = u, ly = layer[a]; a; a = pa[a], --ly) {
            if (auto p = get_pr(a); p.X != -1) pr.erase(p);
            st[flag[u]][a].erase(pll(dis[ly][u], u));
            if (auto p = get_pr(a); p.X != -1) pr.insert(p);
        }
    }
} cent;

int main() {
    ios::sync_with_stdio(0), cin.tie(0);
    int n;
    cin >> n;
    cent.init(n);
    for (int i = 1; i < n; ++i) {
        int u, v, w;
        cin >> u >> v >> w;
        cent.add_edge(u, v, w);
    }
    ll tot = 0;
    for (int i = 1; i <= n; ++i) {
        cin >> org[i] >> tar[i];
        if (org[i] < tar[i]) flag[i] = 1, tot += tar[i] - org[i];
        else if (org[i] > tar[i]) flag[i] = 0;
        else flag[i] = -1;
    }
    cent.build();
    ll ans = 0;
    while (tot--) {
        assert(!pr.empty());
        auto [d, p] = *pr.begin();
        ans += d;
        --org[p.X], ++org[p.Y];
        //cerr << "flow " << p.X << " --> " << p.Y << "\n";
        if (org[p.X] == tar[p.X]) cent.modify(p.X);
        if (org[p.Y] == tar[p.Y]) cent.modify(p.Y);
    }
    cout << ans << "\n";
}