#include <fstream>
#include <vector>
#define MAXC 1010 
#define MAXN 250010
using namespace std;
vector<int> L[MAXC];
vector<pair<int,int> > G[MAXN];
int N,M,X,Y;
int cost[MAXN];



int main(){


	ifstream fi("pscnv.in");
	fi>>N>>M>>X>>Y;
	for (int i=1;i<=M;++i){
		int x,y,z;
		fi>>x>>y>>z;
		G[x].push_back(make_pair(y,z));
		G[y].push_back(make_pair(x,z));
	}
	fi.close();

	for (int i=1;i<=N;++i) cost[i]=MAXC;
	cost[X]=0;
	
	L[0].push_back(X);

	for (int i=0;i<MAXC;++i)
		for (unsigned int j=0;j<L[i].size();++j)
			if (cost[L[i][j]]==i)
				for (vector<pair<int,int> >::iterator it2=G[L[i][j]].begin();it2!=G[L[i][j]].end();++it2)
					if (max(i,it2->second)<cost[it2->first]){
						cost[it2->first]=max(it2->second,i);
						L[max(it2->second,i)].push_back(it2->first);
					}
	
	ofstream fo("pscnv.out");
	fo<<cost[Y]<<"\n";
	fo.close();

	return 0;
}