#include <bits/stdc++.h>
#define Nmax 250005
using namespace std;

class InParser {
private:
    FILE *fin;
    char *buff;
    int sp;

    char read_ch() {
        ++sp;
        if (sp == 4096) {
            sp = 0;
            fread(buff, 1, 4096, fin);
        }
        return buff[sp];
    }

public:
    InParser(const char* nume) {
        fin = fopen(nume, "r");
        buff = new char[4096]();
        sp = 4095;
    }

    InParser& operator >> (int &n) {
        char c;
        while (!isdigit(c = read_ch()) && c != '-');
        int sgn = 1;
        if (c == '-') {
            n = 0;
            sgn = -1;
        } else {
            n = c - '0';
        }
        while (isdigit(c = read_ch())) {
            n = 10 * n + c - '0';
        }
        n *= sgn;
        return *this;
    }
};

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

int N, M, x, y, Max, ans;
bool vis[Nmax], ok;
vector<pair<int, int> > G[Nmax];

void DFS(int node, int len) {
    if (node == y) ok = 1;
    else {
        for (auto it: G[node])
            if (!vis[it.first] && it.second <= len)
                 vis[it.first] = 1, DFS(it.first, len);
    }
}
int main()
{
    fin >> N >> M >> x >> y;
    for (int i = 1; i <= M; ++i) {
        int X, Y, C;
        fin >> X >> Y >> C;
        Max = max(Max, C);
        G[X].push_back({Y, C});
    }

    int le = 1, ri = Max;
    while (le <= ri) {
        int mid = (le + ri) / 2;
        memset(vis, 0, sizeof(vis));
        vis[x] = 1, ok = 0;

        DFS(x, mid);
        if (ok) ans = mid, ri = mid - 1;
        else le = mid + 1;
    }
       fout << ans << '\n';

    return 0;
}