#include <fstream>
#include <string>
#include <cstdlib>
#include <utility>
#include <list>
#include <array>
#include <vector>
#include <queue>
using namespace std;
 
constexpr int inf = 1001;
 
class dial_pq {
    array<queue<int>, inf + 1> buf;
    int poz = 0;
    void clear() {
        while (buf[poz].empty()) {
            ++poz;
        }
    }
 
public:
    void emplace(const int x, const int y) { buf[y].push(x); }
    const pair<int, int> top() {
        clear();
        return make_pair(buf[poz].front(), poz);
    }
    void pop() {
        clear();
        buf[poz].pop();
    }
};
 
int dial(const vector<list<pair<int, int> > > &vecini, const int x,
                 const int y) {
 
    dial_pq st;
    vector<int> rez(vecini.size(), inf);
 
    st.emplace(x, 0);
    rez[x] = 0;
 
    int cur = 0, cost_cur = 0, ipotetic = 0;
 
    while (true) {
        cur = st.top().first;
        cost_cur = st.top().second;
        st.pop();
        if (cur == y) {
            return rez[y];
        }
        if (rez[cur] == cost_cur) {
            for (const auto next : vecini[cur]) {
                ipotetic = max(next.second, cost_cur);
                if (ipotetic < rez[next.first]) {
                    rez[next.first] = ipotetic;
                    st.emplace(next.first, ipotetic);
                }
            }
        }
    }
}
 
void citeste_date(vector<list<pair<int, int> > > &vecini, int &x, int &y) {
    ifstream f("pscnv.in");
    int n, m;
    f >> n >> m >> x >> y >> ws;
    --x, --y;
    vecini.resize(n);
    string buf;
    buf.reserve(256);
    for (int i = 0, a, b, c; i < m; ++i) {
        getline(f, buf);
        char* poz = &buf[0];
        a = strtol(poz, &poz, 10);
        b = strtol(poz, &poz, 10);
        c = strtol(poz, &poz, 10);
        --a, --b;
        vecini[a].emplace_back(b, c);
    }
}
 
int main() {
    vector<list<pair<int, int> > > vecini;
    int x, y;
    citeste_date(vecini, x, y);
    ofstream g("pscnv.out");
    g << dial(vecini, x, y);
    return 0;
}