// beet hieteruka~~~
#include <bits/stdc++.h>

using namespace std;

using int64 = long long;
const int mod = 1e9 + 7;

const int64 infll = (1LL << 62) - 1;
const int inf = (1 << 30) - 1;

struct IoSetup {
  IoSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
  }
} iosetup;


template< typename T1, typename T2 >
ostream &operator<<(ostream &os, const pair< T1, T2 > &p) {
  os << p.first << " " << p.second;
  return os;
}

template< typename T1, typename T2 >
istream &operator>>(istream &is, pair< T1, T2 > &p) {
  is >> p.first >> p.second;
  return is;
}

template< typename T >
ostream &operator<<(ostream &os, const vector< T > &v) {
  for(int i = 0; i < (int) v.size(); i++) {
    os << v[i] << (i + 1 != v.size() ? " " : "");
  }
  return os;
}

template< typename T >
istream &operator>>(istream &is, vector< T > &v) {
  for(T &in : v) is >> in;
  return is;
}

template< typename T1, typename T2 >
inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }

template< typename T1, typename T2 >
inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }

template< typename T = int64 >
vector< T > make_v(size_t a) {
  return vector< T >(a);
}

template< typename T, typename... Ts >
auto make_v(size_t a, Ts... ts) {
  return vector< decltype(make_v< T >(ts...)) >(a, make_v< T >(ts...));
}

template< typename T, typename V >
typename enable_if< is_class< T >::value == 0 >::type fill_v(T &t, const V &v) {
  t = v;
}

template< typename T, typename V >
typename enable_if< is_class< T >::value != 0 >::type fill_v(T &t, const V &v) {
  for(auto &e : t) fill_v(e, v);
}

template< typename F >
struct FixPoint : F {
  FixPoint(F &&f) : F(forward< F >(f)) {}

  template< typename... Args >
  decltype(auto) operator()(Args &&... args) const {
    return F::operator()(*this, forward< Args >(args)...);
  }
};

template< typename F >
inline decltype(auto) MFP(F &&f) {
  return FixPoint< F >{forward< F >(f)};
}

template< typename T >
struct edge {
  int src, to;
  T cost;

  edge(int to, T cost) : src(-1), to(to), cost(cost) {}

  edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}

  edge &operator=(const int &x) {
    to = x;
    return *this;
  }

  operator int() const { return to; }
};

template< typename T >
using Edges = vector< edge< T > >;
template< typename T >
using WeightedGraph = vector< Edges< T > >;
using UnWeightedGraph = vector< vector< int > >;
template< typename T >
using Matrix = vector< vector< T > >;

int main() {
  int N, S, E, T;
  cin >> N >> T >> S >> E;
  --S, --E;
  WeightedGraph< int > g(N);
  for(int i = 1; i < N; i++) {
    int a, b, c;
    cin >> a >> b >> c;
    if(T == 0) c = inf;
    else c = (c + T - 1) / T;
    --a, --b;
    g[a].emplace_back(b, c);
    g[b].emplace_back(a, c);
  }

  vector< int > nxt(N, -1);
  auto rec = MFP([&](auto rec, int idx, int par) -> bool {
    if(idx == E) {
      return true;
    }
    for(auto &to : g[idx]) {
      if(to == par) continue;
      if(rec(to, idx)) {
        nxt[idx] = to;
        return true;
      }
    }
    return false;
  });
  assert(rec(S, -1));


  vector< int > times(N);
  auto rec2 = MFP([&](auto rec2, int idx, int par) -> bool {
    if(~par) times[idx] += 1;
    vector< int > uku;
    for(auto &to : g[idx]) {
      if(to == par) continue;
      if(to == nxt[idx]) continue;
      if(!rec2(to, idx)) return false;
      uku.emplace_back(to.cost - times[to] - 1);
    }
    sort(begin(uku), end(uku));
    for(int i = 0; i < uku.size(); i++) {
      int tap = times[idx] + i;
      if(uku[i] < tap) return false;
    }
    times[idx] += uku.size();
    for(auto &to : g[idx]) {
      if(to == nxt[idx]) {
        if(times[idx] < to.cost) {
          return rec2(nxt[idx], idx);
        } else {
          return false;
        }
      }
    }
    return true;
  });
  if(rec2(S, -1)) {
    cout << "Yes" << endl;
  } else {
    cout << "No" << endl;
  }
}




Measured memory_bytes: 14864