#include <cstdio>
#include <vector>
#include <cstring>
#include <stack>
#include <climits>
#include <algorithm>

using namespace std;

const int nmax = 250000;

struct Dest {
    int nod, cost;
};

vector <Dest> g[1 + nmax];
vector <int> d[1005];
int dist[1 + nmax];
int n, m, ss, ff;

void citire() {
    scanf("%d%d%d%d", &n, &m, &ss, &ff);
    for(int i = 1; i <= m; i ++) {
        int x, y, k;
        scanf("%d%d%d", &x, &y, &k);
        g[x].push_back({y, k});
    }
}

void solve() {
    for(int i = 1; i <= n; i ++)
        dist[i] = INT_MAX;
    dist[ss] = 0;
    d[0].push_back(ss);

    for(int k = 0; k <= 1000; k ++) {
        for(int currentNodeIndex = 0; currentNodeIndex < d[k].size(); currentNodeIndex ++) {
            int currentNode = d[k][currentNodeIndex];
            if(dist[currentNode] == k) {
                for(auto& to: g[currentNode]) {
                    if(dist[to.nod] > max(dist[currentNode], to.cost)) {
                        dist[to.nod] = max(dist[currentNode], to.cost);
                        d[dist[to.nod]].push_back(to.nod);
                    }
                }
            }
        }
    }
}

void afisare() {
    printf("%d", dist[ff]);
}

int main() {
    freopen("pscnv.in", "r", stdin);
    freopen("pscnv.out", "w", stdout);

    citire();
    solve();
    afisare();

    return 0;
}