#include<stdio.h>
#include<vector>
#include<algorithm>

using namespace std;

#define lg 250005

//vector<int> v[lg], vc[lg], cuoada[1005];
int *v[lg], *vc[lg], *cuoada[1005];
int n, m, np, nf, x, y, cst, i, j, k, nod, maxcost, nr[lg], nrp[1005], d[lg];
void citire(){
	int kkt = 0, j, nt;
	char sir[50];
	fgets(sir, 50, stdin), nt = 0;
	
	for (j = nt; sir[j] <= '9' && sir[j] >= '0'; j ++)
		kkt = kkt*10+sir[j]-'0';
	x = kkt, kkt = 0;
	nt = j+1;
	for (j = nt; sir[j] <= '9' && sir[j] >= '0'; j ++)
		kkt = kkt*10+sir[j]-'0';
	y = kkt, kkt = 0;
	nt = j+1;
	for (j = nt; sir[j] <= '9' && sir[j] >= '0'; j ++)
		kkt = kkt*10+sir[j]-'0';
	cst = kkt;
}
int main()
{
	freopen("pscnv.in", "rt", stdin);
	freopen("pscnv.out", "wt", stdout);
	
	scanf("%d%d%d%d\n", &n, &m, &np, &nf);
	for (i = 1; i <= m; i ++){
		//scanf("%d%d%d", &x, &y, &cst);
		citire();
		
		if (x != y){
			nr[x] ++;
			/*
			v[x].push_back(y);
			vc[x].push_back(cst);
			*/
			v[x] = (int*)realloc(v[x], (nr[x]+1)*sizeof(int));
			vc[x] = (int*)realloc(vc[x], (nr[x]+1)*sizeof(int));
			v[x][nr[x]] = y;
			vc[x][nr[x]] = cst;
			maxcost = max(maxcost, cst);
		}
	}
	
	nrp[0] = 1;
	//cuoada[0].push_back(np);
	cuoada[0] = (int*)realloc(cuoada[0], (nrp[0]+1)*sizeof(int));
	cuoada[0][1] = np;
	d[np] = 0;
	for (i = 0; i <= maxcost; i ++)
		for (j = 1; j <= nrp[i]; j ++){
			x = cuoada[i][j];
			if (x == nf){
				printf("%d\n", i);
				return 0;
			}
			if (d[x] == i)
				for (k = 1; k <= nr[x]; k ++){
					nod = v[x][k];
					cst = vc[x][k];
					
					if (cst < i){
						nrp[i] ++;
						//cuoada[i].push_back(nod);
						cuoada[i] = (int*)realloc(cuoada[i], (nrp[i]+1)*sizeof(int));
						cuoada[i][nrp[i]] = nod;
						if ((d[nod] == 0 && nod != np) || d[nod] > i)
							d[nod] = i;
					}
					else{
						nrp[cst] ++;
						//cuoada[cst].push_back(nod);
						cuoada[cst] = (int*)realloc(cuoada[cst], (nrp[cst]+1)*sizeof(int));
						cuoada[cst][nrp[cst]] = nod;
						if ((d[nod] == 0 && nod != np) || d[nod] > cst)
							d[nod] = cst;
					}
				}
		}
	
	return 69;
}