#include <fstream>
#include <vector>
#include <queue>
#include <utility>
#include <algorithm>
#include <cstring>
#include <cstdlib>

const int MAX_N(250001);
const int MAX_K(1001);

int n, m, x, y;
int Dp [MAX_N];
std::vector<std::pair<int,int>> Graph [MAX_N];
char s [20];

inline void Read (void)
{
	std::ifstream input("pscnv.in");
	input >> s;
	n = std::atoi(s);
	input >> s;
	m = std::atoi(s);
	input >> s;
	x = std::atoi(s);
	input >> s;
	y = std::atoi(s);
	for (int i(1), a, b, c ; i <= m ; ++i)
	{
		input >> s;
		a = std::atoi(s);
		input >> s;
		b = std::atoi(s);
		input >> s;
		c = std::atoi(s);
		Graph[a].push_back(std::make_pair(b,c));
	}
	input.close();
}

inline void Print (void)
{
	std::ofstream output("pscnv.out");
	output << Dp[y] << '\n';
	output.close();
}

inline void Dynamic (void)
{
	int vertex(1), c;
	std::queue<int> queue [MAX_K];
	queue[0].push(x);
	std::memset(Dp + 1,0x3f3f3f3f,sizeof(*Dp) * n);
	Dp[x] = 0;
	int i(0), node;
	while (vertex)
	{
		while (i < MAX_K && queue[i].empty())
			++i;
		if (i == MAX_K)
			break;
		node = queue[i].front();
		queue[i].pop();
		--vertex;
		for (auto it : Graph[node])
		{
			c = std::max(Dp[node],it.second);
			if (Dp[it.first] > c)
			{
				Dp[it.first] = c;
				++vertex;
				queue[c].push(it.first);
			}
		}
	}
}

int main (void)
{
	Read();
	Dynamic();
	Print();
	return 0;
}