#include "bits/stdc++.h"
#define YES "YES"
#define NO "NO"
#define YESNO OUT(three(solve(),YES,NO))
#define ECHO OUT(solve())
#define three(A,B,C) ((A)?(B):(C))
#define FOR(i,a,b)  for(LL i=(a);i< (LL)(b);i++)
#define EFOR(i,a,b) for(LL i=(a);i<=(LL)(b);i++)
#define RFOR(i,a,b) for(LL i=(b);i>=(LL)(a);i--)
#define REP(i,b) FOR(i,zero,b)
#define rep REP
#define EREP(i,b) EFOR(i,zero,b)
#define RREP(i,b) RFOR(i,b,zero)
#define ALL(c) c.begin(),c.end()
#define UNIQUE(c) sort(ALL(c));c.erase(unique(ALL(c)),c.end())
#define MAX(c) (*max_element(ALL(c)))
#define MIN(c) (*min_element(ALL(c)))
#define MP make_pair
#define FI first
#define SE second
#define SI(x) (LL(x.size()))
#define PB push_back
#define DEBUG(a) OUT(a)
#define DEBUG2(a,b) OUT2(a,b)
#define cat cout << __LINE__ << endl
#define OUT(a) cout << (a) << endl
#define OUT2(a,b) cout << (a) <<" "<<(b) << endl
#define zero 0LL
#define all ALL
#define pb emplace_back
#define eb pb
#define int long long
using namespace std;
template<typename T> inline void maximize(T &a, T b) { a = max(a, b); }
template<typename T> inline void minimize(T &a, T b) { a = min(a, b); }
template<typename T> inline bool middle(T a, T b, T c) { return b <= a && a <= c; }
template<class T> inline bool MX(T &l, const T &r) { return l < r ? l = r, 1 : 0; }
template<class T> inline bool MN(T &l, const T &r) { return l > r ? l = r, 1 : 0; }
typedef int LL;
typedef double ld;
typedef int ut;
typedef vector<ut> VI;
typedef vector<VI> VII;
typedef pair<ut, ut> pr;
typedef pair<ut, pr> ppr;
typedef vector<pr> Vpr;
typedef vector<ppr> Vppr;
typedef tuple<int, int, int, int> tapu;
typedef vector<tapu> Vtapu;
typedef priority_queue<tapu, Vtapu, greater<tapu> > PQ;
inline void outputVI(VI x) { REP(i, SI(x)) { cout << three(i, " ", "") << x[i]; }OUT(""); }
const int SIZE1 = 3e5 + 1000;
const int SIZE2 = 5010;
const int SIZE3 = 430;
const int SIZE = SIZE1;
const int MAPSIZE = 40;
const LL p = 7 + 1e9;
const LL INF = 1LL << 60;
const long double EPS = 1e-7;
typedef pair<ld, ut> pld;
 
int dx[]={0,0,1,-1};
int dy[]={-1,1,0,0};
LL N,T,S,E;
Vpr edges[SIZE];
Vpr nedges[SIZE];
LL to[SIZE];
LL fromlimit[SIZE];
LL tolimit[SIZE];
LL used[SIZE];
LL dfsed(int now,int from){
  for(auto ne:edges[now]){
    LL next=ne.second;
    if(next==from){
       fromlimit[now]=ne.first;
       continue;
    }
    if(dfsed(next,now)){
      to[now]=next;
      tolimit[now]=ne.first;
      return 1;
    }
  }
  if(now==E) return 1;
  to[now]=from;
  tolimit[now]=fromlimit[now];
  return 0;
}
LL dfs(int now,int from){
  sort(ALL(nedges[now]));
  if(from!=-1) used[now]+=T; 
  
  for(auto ne:nedges[now]){
    LL next=ne.second;
//    cout << ne.first <<" " << next << endl;
    if(next==from or to[now]==next) continue;
    if(used[now]>=ne.first){
      return 1;
    }
    if(dfs(next,now)){
      return 1; 
     
    }
    used[now]+=T;
  }
  if(now==E) return 0;
  for(auto ne:edges[now]){
    LL next=ne.second;
    if(to[now]!=next) continue;
//    cout << used[1] << " " << used[2] << endl;
    if(used[now]+used[next]>=ne.first){
      return 1;
    
    }
//    cout << to[now] << endl;
    if(to[now]!=from and dfs(next,now)){
      return 1; 
     
    }
  }
  return 0;
}
signed main(){
  cin >> N >> T >> S >> E;
  REP(i,N-1){
    LL a,b,c;
    cin >> a >> b >> c;
    edges[a].pb(c,b);
    edges[b].pb(c,a);
  }
  fromlimit[S]=INF;
  dfsed(S,-1);
  EFOR(i,1,N)
    for(auto ne:edges[i]){
      if(ne.second==to[i]) continue;
      nedges[i].pb(ne.first-T*(LL)edges[ne.second].size(),ne.second);
    }
  if(dfs(S,-1)){
    cout << "No" << endl;
  }else cout << "Yes" << endl;
  return 0;
}



Measured memory_bytes: 30944