#include <fstream>
#include <vector>
#include <algorithm>
#include <cstring>

using namespace std;

ifstream fin("pscnv.in");
ofstream fout("pscnv.out");

const int dim = 250100;
const int inf = 1005;

int nodeCount, edgeCount, source, destination;
vector< pair<int, int> > graph[dim];

int dp[dim];
vector<int> lists[inf];

int Dijkstra() {

    for (int i = 1; i <= nodeCount; ++i)
        dp[i] = inf;

    dp[source] = 0;
    lists[0].push_back(source);

    for (int i = 0; i < inf; ++i) {
        for (auto it = lists[i].begin(); it != lists[i].end(); ++it) {

            int curr = *it;

            if (dp[curr] < i)
                continue;

            if (curr == destination)
                return i;

            for (auto adj : graph[curr]) {
                int aux = max(dp[curr], adj.second);
                if (dp[adj.first] <= aux)
                    continue;
                dp[adj.first] = aux;
                lists[aux].push_back(adj.first);
            }

        }
    }

    return inf;

}

int main() {

    fin >> nodeCount >> edgeCount >> source >> destination;

    for (int i = 1; i <= edgeCount; ++i) {
        int x, y, cost;
        fin >> x >> y >> cost;
        graph[x].push_back(make_pair(y, cost));
    }

    fout << Dijkstra() << '\n';

    return 0;

}

//Trust me, I'm the Doctor!