// By Stefan Radu

#include <bits/stdc++.h>

using namespace std;

#define sz(x) (int)(x).size()

typedef pair < int, int > pii;
typedef long long ll;
typedef long double ld;
typedef unsigned int ui;
typedef unsigned long long ull;

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

struct Edge {
  int nei, weight;
};

vector < bool > used;
vector < vector < Edge > > gr;

bool getMost(int node, int y, int &most) {

  if (node == y) return true;

  used[node] = true;
  for (auto edge : gr[node]) {
    if (used[edge.nei]) continue;

    most = max(most, edge.weight);
    if (getMost(edge.nei, y, most)) return true;
  }

  return false;
}

int main() {

#ifdef STEF
  freopen("input", "r", stdin);
  freopen("output", "w", stdout);
#endif

  ios::sync_with_stdio(false);
  cin.tie(0);cout.tie(0);


  int n, m, x, y;
  fin >> n >> m >> x >> y;

  gr.resize(n + 1);
  used.resize(n + 1);
  for (int i = 1; i <= m; ++ i) {
    int a, b, c;
    fin >> a >> b >> c;
    gr[a].push_back({b, c});
  }

  for (int i = 1; i <= n; ++ i) {
    sort(gr[i].begin(), gr[i].end(), [](Edge a, Edge b) -> bool {
        return a.weight < b.weight;
    });
  }

  int most = -1;
  getMost(x, y, most);
  fout << most << '\n';
}