#include<cstdio>
#include<cstring>
#include<cmath>
#include<ctime>
#include<string>
#include<vector>
#include<queue>
#include<deque>
#include<set>
#include<list>
#include<stack>
#include<bitset>
#include<algorithm>
#define INF (1 << 30)
#define pb push_back
#define mkp make_pair
#define pii pair<int, int>
#define ll long long
#define nxt (*it).first
#define cst (*it).second
#define type int
#define FOR(i,a,b)\
   for(int i=a; i<=b; ++i)
#define FORR(i,a,b)\
   for(int i=a; i>=b; --i)
#define ALLR(g) \
   for(typeof(g.rbegin()) it=g.rbegin(); it!=g.rend(); ++it)
#define ALL(g)\
   for(typeof(g.begin()) it=g.begin(); it!=g.end(); ++it)
#define infile "pscnv.in"
#define outfile "pscnv.out"
#define nMax 250005
using namespace std;

vector < pii > v[nMax];

int D[nMax];

int N, M, X, Y;

void read(){
    freopen(infile, "r", stdin);

    scanf("%d %d %d %d\n", &N, &M, &X, &Y);

    char S[50];

    int x, y, cost;
    FOR(i,1,M){
    	gets(S);
    	sscanf(S, "%d %d %d", &x, &y, &cost);

    	v[x].pb(mkp(y,cost));
    }

    fclose(stdin);
}

void Dijkstra(){
	priority_queue < pii > PQ;

	FOR(i,0,N)
	   D[i] = INF;

	PQ.push(mkp(D[X] = 0, X));

	while(!PQ.empty()){
		int x = PQ.top().second;
		int dx = PQ.top().first;
		PQ.pop();

		if(D[x] < -dx)
			continue;

		ALL(v[x])
		   if(max(D[x], cst) < D[nxt]){
			   D[nxt] = max(D[x], cst);

			   PQ.push(mkp(-D[nxt], nxt));
		   }
	}
}

void print(){
    freopen(outfile, "w", stdout);

    printf("%d\n", D[Y]);

    fclose(stdout);
}

int main(){
    read();

    Dijkstra();

    print();

    return 0;
}