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#include<bits/stdc++.h>
using namespace std;
#ifdef LOCALd
#define debug(...) fprintf(stdout, ##__VA_ARGS__)
#else
#define debug(...) void(0)
#endif
#define ll long long
inline int read(){int x=0,f=1;char ch=getchar(); while(ch<'0'||
ch>'9'){if(ch=='-')f=-1;ch=getchar();}while(ch>='0'&&ch<='9'){
x=(x<<1)+(x<<3)+(ch^48);ch=getchar();}return x*f;}
#define Z(x) (x)*(x)
#define pb push_back
#define fi first
#define se second
#define N 800010
struct Point { int x; ll w; int o; };
int n, m, i, j, k, T;
ll ans=-1e18, c, C;
int Log2[N], ST, ED;
struct node { int x, dep; };
node min(node A, node B) { return A.dep < B.dep ? A : B; }
int min(int a, int b) { return a < b ? a : b; }
node f[N][20];
struct Tree_ {
int i, m;
struct edge { int y; ll z; };
vector<edge>G[N];
int dfn[N], tot, l, r;
int h[N], oula[N], oula_xu[N];
ll dep[N];
void add_edge(int x, int y, ll z) {
debug("%d %d %d\n", x, y, z);
G[x].pb({y, z}); G[y].pb({x, z});
}
void dfs1(int x, int fa) {
h[x] = h[fa] + 1; dfn[x] = ++tot;
oula[++m] = x; oula_xu[x]=m;
for(auto t : G[x]) if(t.y != fa) {
int y = t.y, z = t.z; dep[y] = dep[x] + z;
dfs1(y, x); oula[++m] = x;
}
}
void Pre_Lca() {
for(i=2; i<=m; ++i) Log2[i]=Log2[i>>1]+1;
for(i=1; i<=m; ++i) f[i][0]={oula[i], h[oula[i]]};
for(k=1; k<=19; ++k)
for(l=1, r=(1<<k); r<=m; ++l, ++r)
f[l][k]=min(f[l][k-1], f[l+(1<<k-1)][k-1]);
}
int lca(int x, int y) {
int a = oula_xu[x], b = oula_xu[y];
if(a > b) swap(a, b);
int k = Log2[b - a + 1];
return min(f[a][k], f[b-(1<<k)+1][k]).x;
}
}T1, T2;
namespace Tree2 {
void Read() {
int u, v, i; ll w;
for(i=1; i<n; ++i) {
u=read(); v=read(); w=read();
T2.add_edge(u, v, w);
}
T2.dfs1(1, 0);
for(i=1; i<=T2.m; ++i) debug("%d ", T2.oula[i]); debug("\n");
for(i=1; i<=n; ++i) debug("%d ", T2.oula_xu[i]); debug("\n");
T2.Pre_Lca();
}
int sta[N], top, l, O[N>>1];
ll w[N>>1];
vector<pair<int, int> >E;
vector<int>G[N>>1];
void build(vector<Point>h) {
sta[top=1]=1; E.clear();
debug("Point : "); for(auto t : h) debug("%d ", t.x); debug("\n");
for(auto t : h)
if(t.x != 1) {
l = T2.lca(t.x, sta[top]);
debug("Lca(%lld %lld) %lld\n", t.x, sta[top], l);
if(sta[top] != l) {
while(T2.dfn[sta[top-1]] > T2.dfn[l])
E.pb({sta[top-1], sta[top]}), --top;
if(sta[top-1] != l) E.pb({l, sta[top]}), sta[top]=l;
else E.pb({l, sta[top]}), --top;
}
sta[++top] = t.x;
}
while(top > 1) E.pb({sta[top-1], sta[top]}), --top;
for(auto t : E) G[t.fi].clear(), G[t.se].clear(), O[t.fi]=O[t.se]=0;
for(auto t : E) G[t.fi].pb(t.se), debug("%d -> %d\n", t.fi, t.se);
for(auto t : h) O[t.x]=t.o, w[t.x]=t.w;
}
ll dp[N][2];
void dfs(int x) {
dp[x][0] = dp[x][1] = -1e12;
if(O[x] == 1) dp[x][0] = w[x];
if(O[x] == 2) dp[x][1] = w[x];
for(int y : G[x]) {
dfs(y);
ans = max(ans, dp[x][0] + dp[y][1] - 2 * T2.dep[x] + c);
ans = max(ans, dp[x][1] + dp[y][0] - 2 * T2.dep[x] + c);
dp[x][0] = max(dp[x][0], dp[y][0]);
dp[x][1] = max(dp[x][1], dp[y][1]);
}
}
void solve(vector<Point>h) {
build(h); dfs(1);
}
}
namespace Tree1 {
vector<pair<int, ll> >G[N>>1];
int tot, b[N], O[N];
ll mx[N], w[N], sum, dis[N];
void dfs(int x, int fa) {
for(auto t : G[x]) if(t.fi!=fa) {
int y = t.fi, z = t.se;
if(!b[x]) b[x]=++tot, T1.add_edge(x, b[x], 0);
else T1.add_edge(b[x], tot+1, 0), b[x]=++tot;
T1.add_edge(b[x], y, z);
dfs(y, x);
}
}
int rt;
void Build() {
tot=n;
int u, v; ll w;
for(i=1; i<n; ++i) {
u=read(); v=read(); w=read();
G[u].pb({v, w}); G[v].pb({u, w});
}
dfs(1, 0); T1.dfs1(1, 0);
mx[0]=1e18;
debug("-------\n");
memset(b, 0, sizeof(b));
}
void dfs2(int x, int fa) {
w[x]=1;
for(auto t : T1.G[x]) if(t.y!=fa && !b[t.y]) {
int y = t.y, z = t.z;
dfs2(y, x); w[x]+=w[y];
if(mx[y] < mx[rt]) rt=y, ST=x, ED=y, C=z;
}
mx[x]=max(w[x], sum-w[x]);
}
void dfs3(int x, int fa, int o) {
O[x]=o;
for(auto t : T1.G[x]) if(t.y != fa && !b[t.y]) {
int y = t.y, z = t.z; dis[y] = dis[x] + z;
dfs3(y, x, o);
}
}
vector<Point>h;
void solve(int x, vector<int>a) {
dfs2(x, 0); sum=w[x]; rt=0; dfs2(x, 0);
if(sum == 1) return ;
int st = ST, ed = ED; c = C;
debug("{%lld}%lld [%lld %lld] %lld\n", x, sum, st, ed, c);
vector<int>va, vb;
dis[st]=dis[ed]=0;
dfs3(st, ed, 1); dfs3(ed, st, 2);
h.clear();
for(auto u : a) {
h.pb({u, dis[u]+T1.dep[u], O[u]});
debug("%lld : %lld | %lld\n", u, dis[u]+T1.dep[u], O[u]);
if(O[u] == 1) va.pb(u);
if(O[u] == 2) vb.pb(u);
}
a.clear();
if(va.size() && vb.size()) Tree2 :: solve(h);
b[ed]=1; solve(st, va); b[ed]=0; va.clear();
b[st]=1; solve(ed, vb); b[st]=0; vb.clear();
}
void Main() {
vector<int>a;
for(i=1; i<=n; ++i) a.pb(i);
sort(a.begin(), a.end(), [] (int x, int y) { return T2.dfn[x] < T2.dfn[y]; });
for(auto t : a) debug("%d ", t); debug("\n");
solve(1, a);
}
}
signed main()
{
#ifdef LOCALd
freopen("in.txt", "r", stdin);
freopen("out.txt", "w", stdout);
#endif
n=read();
Tree1::Build();
Tree2::Read();
Tree1::Main();
assert(ans%2==0);
ans/=2;
for(i=1; i<=n; ++i) ans=max(ans, (2*T1.dep[i]-(T1.dep[i]+T2.dep[i])));
printf("%lld", ans);
return 0;
}
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