#include <fstream>
#include <algorithm>
#include <vector>
#include <queue>
#include <sstream>

using namespace std;

#define DIM 5000000
char buff[DIM];
int poz = 0;

inline int nextInt() {
	int numar = 0;
	while (buff[poz] < '0' || buff[poz] > '9')
	
	if (++poz == DIM)
		fread(buff, 1, DIM, stdin), poz = 0;
     
	while ('0' <= buff[poz] && buff[poz] <= '9') {
		numar = numar * 10 + buff[poz] - '0';
		if (++poz == DIM)
			fread(buff, 1, DIM, stdin), poz = 0;
	}
	return numar;
}

const int nmax = (1 << 18) - 1;
vector< int > graph[nmax];

int main()
{
	freopen("pscnv.in", "r", stdin);
	freopen("pscnv.out", "w", stdout);
	int n, m, x, y;
	queue<int> q;
	vector<bool> visited;
	
	n = nextInt(); m = nextInt(); x = nextInt(); y = nextInt();
	x--;
	y--;

	visited.resize(n);

	for (int a, b, c; m; m--) {
		a = nextInt(); b = nextInt(); c = nextInt();
		a--;
		b--;
		graph[a].push_back(b | c << 18);
	}

	int l = 1, r = 1000;
	while (l <= r) {
		int mid = (l + r) / 2;
		fill(visited.begin(), visited.end(),false);
		visited[x] = true;
		q.push(x);
		while (!q.empty() && !visited[y]) {
			int v = q.front();
			q.pop();
			for (const int& w : graph[v]) {
				if ( (w >> 18) <= mid && !visited[w & nmax]) {
					visited[w & nmax] = true;
					q.push(w & nmax);
				}
			}
		}

		while (!q.empty()) q.pop();

		if (visited[y]) {
			r = mid - 1;
		} else {
			l = mid + 1;
		}
	}

	printf("%d\n", l);
	return 0;
}