#if __has_include("../library/Basic/Debug.hpp")

#include "../library/Basic/Debug.hpp"

#else

/* ----- Header Files ----- */
// IO
#include <cstdio>
#include <iomanip>
#include <ios>
#include <iostream>

// algorithm
#include <algorithm>
#include <cmath>
#include <numeric>

// container
#include <vector>
#include <string>
#include <tuple>
#include <complex>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <bitset>

// others
#include <random>
#include <limits>
#include <functional>
#include <ctime>
#include <cassert>
#include <cstdint>

/* ----- Type Alias ----- */
using Int = long long int;
using Real = long double;
using std::pair;
using std::string;
using std::tuple;
using std::vector;
template <class T>
using MaxHeap = std::priority_queue<T>;
template <class T>
using MinHeap = std::priority_queue<T, std::vector<T>, std::greater<T>>;

template <class T>
T genv(T v) { return v; }

template <class T, class... Ts>
auto genv(size_t l, Ts... ts) {
    return vector<decltype(genv<T>(ts...))>(l, genv<T>(ts...));
}

template <class Cost = Int>
struct Edge {
    Int src, dst;
    Cost cost;
    Edge(Int src = -1, Int dst = -1, Cost cost = 1)
        : src(src), dst(dst), cost(cost){};

    bool operator<(const Edge<Cost>& e) const { return this->cost < e.cost; }
    bool operator>(const Edge<Cost>& e) const { return this->cost > e.cost; }
};

template <class Cost = Int>
using Edges = vector<Edge<Cost>>;
template <class Cost = Int>
using Graph = vector<vector<Edge<Cost>>>;

#endif

/* ----- Misc ----- */
void fastio() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
}

struct Fout {
    Int precision;
    Fout(Int precision) : precision(precision) {}
};
std::ostream& operator<<(std::ostream& os, const Fout& fio) {
    os << std::fixed << std::setprecision(fio.precision);
    return os;
}


/* ----- Constants ----- */
// constexpr Int INF = std::numeric_limits<Int>::max() / 3;
// constexpr Int MOD = 1000000007;
// const Real PI = acos(-1);
// constexpr Real EPS = 1e-10;
// std::mt19937 mt(int(std::time(nullptr)));

using std::function;

void fail() {
    std::cout << "No" << std::endl;
    std::exit(0);
}

int main() {
    int n, t, s, g;
    std::cin >> n >> t >> s >> g;
    --s, --g;

    Graph<Int> tree(n);
    for (int i = 0; i < n - 1; ++i) {
        int u, v;
        Int w;
        std::cin >> u >> v >> w;
        --u, --v;
        tree[u].emplace_back(u, v, w);
        tree[v].emplace_back(v, u, w);
    }

    function<bool(int, int)> dfs = [&](int v, int p) {
        MinHeap<pair<Int, Edge<Int>>> heap;
        Edge<Int> last(-1);

        for (auto e : tree[v]) {
            if (e.dst == p) continue;
            bool isgoal = dfs(e.dst, e.src);
            if (isgoal) {
                last = e;
            } else {
                heap.emplace(e.cost - tree[e.dst].size() * t, e);
            }
        }

        Int damage = (p >= 0 ? t : 0);
        // 入ってくるときに1
        while (!heap.empty()) {
            Int w;
            Edge<Int> e;
            std::tie(w, e) = heap.top();
            heap.pop();
            if (w <= damage) fail();
            damage += t;
        }

        if (last.src != -1) {
            if (last.cost <= damage) fail();
        }
        return (v == g || last.src != -1);
    };
    dfs(s, -1);

    std::cout << "Yes" << std::endl;
    return 0;
}



Measured memory_bytes: 19844