#include <stdio.h>

int n, m, sursa, dest, ok;

typedef struct nod
{
	int x, c;
	nod *a;
} *pNod;
pNod v[250006];

void citire()
{
	freopen("pscnv.in","r",stdin);
	freopen("pscnv.out","w",stdout);

	char s[100];
	scanf("%d %d %d %d\n",&n,&m,&sursa,&dest);

	int i, a, b, c, j;
	pNod q;
	for (i = 1; i <= m; i++)
	{
		fgets(s,100,stdin);
		j = a = b = c = 0;
		while (s[j] <= '9' && s[j] >= '0') {a = a * 10 + s[j] - '0'; j++;}
		j++;
		while (s[j] <= '9' && s[j] >= '0') {b = b * 10 + s[j] - '0'; j++;}
		j++;
		while (s[j] <= '9' && s[j] >= '0') {c = c * 10 + s[j] - '0'; j++;}
		
		q = new nod;
		q -> x = b;
		q -> c = c;
		q -> a = v[a];
		v[a] = q;
	}
}

void DF(int nod, int d)
{
	pNod p;
	if (nod == dest) ok = 1; 
	if (ok)return;
	for (p = v[nod]; p != NULL; p = p -> a)
		if (p -> c <= d) DF(p -> x, d);
}

int caut()
{
	int p = 1, u = 1000, m, i;
	while (1 << i <= m) i++;
	m = 1 << (i - 1);

	while (p <= u)
	{
		ok = 0;
		DF(sursa, m);
		if (ok) 
		{
			ok = 0;
			DF(sursa, m - 1);
			if (!ok) return m;
			else 
			{
				i = 0;
				u = m - 1;
				while (p + (1 << i) <= u) i++;
				m = p + (1 << (i - 1));
			}
		}
		else 
		{
			p = m + 1;
			while (p + (1 << i) <= u) i++;
			m = p + (1 << (i - 1));
		}

	}
	return 0;
}

int main()
{
	citire();
	printf("%d\n",caut());
	return 0;
}