#include <bits/stdc++.h>
#define ll long long
#define SZ(X) (int)(X.size())
#define MAX 200005
#define VAL 1000006
#define pii pair <int,int>
#define node first
#define wei second
using namespace std;

struct Data{
    ll cost;
    int score;
    Data operator + (const Data & other) const {
        return {cost+other.cost, score+other.score};
    }
    void operator += (const Data & other){
        *this = *this + other;
    }
};

struct SegmentTree{
    Data data[VAL*4];
    int len = VAL-1;
    Data merge(Data x, Data y){ // change
        return x+y;
    }
     
    void initialize(int loc, int le, int ri, Data arr[]){
        if (le == ri) data[loc] = arr[le];
        else {
            int mid = (le+ri)/2;
            initialize(loc*2, le, mid, arr);
            initialize(loc*2+1, mid+1, ri, arr);
            data[loc] = merge(data[loc*2], data[loc*2+1]);
        }
    }
     
    void update(int loc, int ind, int le, int ri, Data arr[]){
        if (le == ri) data[loc] = arr[le];
        else {
            int mid = (le+ri)/2;
            if (ind <= mid) update(loc*2, ind, le, mid, arr);
            else update(loc*2+1, ind, mid+1, ri, arr);
            data[loc] = merge(data[loc*2], data[loc*2+1]);
        }
    }
     
    int query(ll targ, int loc, int le, int ri){ // binary search query
        if (le == ri) return data[loc].score;
        int mid = (le+ri)/2;
        if (targ <= data[loc*2].cost) return query(targ, loc*2, le, mid);
        else return query(targ-data[loc*2+1].cost, loc*2+1, mid+1, ri) + data[loc*2+1].score;
    }
};

int caseNum;
int nodeNum, cityA, cityB;
ll lim;
vector <pii> edge[MAX];
ll dist[MAX][2];
int ans;
int a, b, c;

SegmentTree seg;
Data arr[VAL];
vector <pii> opt; // b (cost for reachable from both), a (cost for reachable from one)

void reset(){
    for (int i = 0; i < nodeNum; i++){
        edge[i].clear();
        dist[i][0] = dist[i][1] = 0;
    }
    for (int i = 0; i < VAL; i++)
        arr[i] = {0,0};
    opt.clear();
    ans = 0;
}

void dfs(int cur, int par, bool which){ // for each node, find distance from the two cities
    for (pii nex : edge[cur]){
        if (nex.node == par) continue;
        dist[nex.node][which] = dist[cur][which] + nex.wei;
        dfs(nex.node, cur, which);
    }
}

void enumOverlap(){ // check options for overlap
    for (int i = 0; i < nodeNum; i++){ // assume each node -> reachable to at most one city
        opt.push_back({max(dist[i][0], dist[i][1]), min(dist[i][0], dist[i][1])});
        arr[opt.back().second] += {opt.back().second, 1}; // put in a's
    }
    seg.initialize(1, 1, seg.len, arr);
    sort(opt.begin(), opt.end()); // sort by max distance
    ans = max(ans, seg.query(lim, 1, 1, seg.len));
    //cout << seg.data[1].cost << " " << dist[1][1] << " " << ans << "\n";
    Data defa = {0,0}; // default (pick none)
    for (pii o : opt){ // each node before o -> reachable to at least one city
        defa += {o.second, 1};
        if (defa.cost > lim) return;
        arr[o.second] += {-o.second, -1};
        arr[o.first-o.second] += {o.first-o.second, 1};
        ans = max(ans, seg.query(lim-defa.cost, 1, 1, seg.len)+defa.score);
    }
}
/*
void solve(){
    cin >> nodeNum >> cityA >> cityB >> lim;
    reset();
    for (int i = 0; i < nodeNum-1; i++){
        cin >> a >> b >> c;
        edge[a].push_back({b, c});
        edge[b].push_back({a, c});
    }
    dfs(cityA, -1, 0);
    dfs(cityB, -1, 1);

    enumOverlap();
    
    cout << ans << "\n";
}
int main() {
    ios::sync_with_stdio(0); cin.tie(0);
     
    return 0;
}
*/


int max_score(int nodeNum, int cityA, int cityB, ll lim, int U[], int V[], int W[]){
    reset();
    for (int i = 0; i < nodeNum-1; i++){
        edge[U[i]].push_back({V[i], W[i]});
        edge[V[i]].push_back({U[i], W[i]});
    }
    dfs(cityA, -1, 0);
    dfs(cityB, -1, 1);

    enumOverlap();
    
    return ans;
}

/usr/bin/ld: /tmp/cc49bKfX.o: in function `main':
implementer.cpp:(.text.startup+0x744): undefined reference to `max_score(int, int, int, long long, std::vector<int, std::allocator<int> >, std::vector<int, std::allocator<int> >, std::vector<int, std::allocator<int> >)'
collect2: error: ld returned 1 exit status