#include <bits/stdc++.h>
using namespace std;
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define fo(i, n) rep(i, 0, n)
#define all(x) std::begin(x), std::end(x)
#define sz(x) int((x).size())
#define F first
#define S second
#define MP make_pair
#define PB push_back
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;
typedef vector<vi> vvi;
typedef vector<pii> vpii;
typedef vector<ll> vll;
typedef pair<ll, ll> pll;
typedef vector<vll> vvll;
typedef vector<pll> vpll;
typedef vector<double> vd;
typedef pair<double, double> pdd;
typedef vector<vd> vvd;
typedef vector<pdd> vpdd;

int n, k;
vi diffs;
vvi g;

vector<pair<pii, int>> t1, t2;

int dfs(int u, int p) {
	int o = diffs[u];
	for (int v: g[u]) {
		if (v == p) continue;
		o += dfs(v, u);
	}
	if (o > 0) {
		t1.PB({{u, p}, o});
	} else if (o < 0) {
		t2.PB({{p, u}, -o});
	}
	return o;
}

signed main()
{
    cin.tie(0)->sync_with_stdio(0);
    cin.exceptions(cin.badbit | cin.failbit);
    cin >> n;
    g = vvi(n);
    diffs = vi(n, 0);
    fo(_,n-1) {
	    int a, b;
	    cin >> a >> b;
	    g[a].PB(b);
	    g[b].PB(a);
    }
    cin >> k;
    fo(i, k) {
	    int a; cin >> a;
	    diffs[a]++;
    }
    fo(i, k) {
	    int a; cin >> a;
	    diffs[a]--;
    }

    assert(dfs(0, -1) == 0);
    reverse(all(t2));
    cout << t1.size() + t2.size() << "\n";

    for (auto x: t1) {
	    cout << x.F.F << " " << x.F.S << " " << x.S << "\n";
    }
    for (auto x: t2) {
	    cout << x.F.F << " " << x.F.S << " " << x.S << "\n";
    }
}