#include <stdio.h>
#include <vector>

using namespace std;

vector <pair <int, int> > G[250500];
vector <int> dmin[1024];
int sol[250500];

const int DIM = 1 << 13;
char buff[DIM];
int poz = 0;

void read (int &numar)
{
    numar = 0;
    while (buff[poz] < '0' || buff[poz] > '9')
        if (++poz == DIM)
            fread(buff,1,DIM,stdin),poz=0;

    while ('0'<=buff[poz] && buff[poz]<='9')
    {
        numar = numar*10 + buff[poz] - '0';
        if (++poz == DIM)
            fread(buff,1,DIM,stdin),poz=0;
    }

}

inline int max(int A, int B)
{
    if (A > B)
        return A;
    return B;
}

void relax(int nod)
{
    vector <pair <int, int> > :: iterator it;

    for (it = G[nod].begin(); it != G[nod].end(); it ++)
        if (max(sol[nod], it -> second) < sol[it -> first])
        {
            sol[it -> first] = max(sol[nod], it -> second);
            dmin[max(sol[nod], it -> second)].push_back(it -> first);
        }
}

int main()
{
    int i, j, N, M, X, Y, maxC = 0;

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

    read(N); read(M); read(X); read(Y);
    for (i = 1; i <= M; i ++)
    {
        int x0, y0, c;

        read(x0); read(y0); read(c);
        G[x0].push_back(make_pair(y0, c));
        if (c > maxC)
            maxC = c;
    }

    vector <int> :: iterator it;

    for (i = 1; i <= N; i ++)
        sol[i] = 1 << 30;
    sol[X] = 0; relax(X);

    for (i = 1; i <= maxC; i ++)
        for (j = 0; j < dmin[i].size(); j ++)
        {
            if (dmin[i][j] == Y)
            {
                printf("%d", sol[Y]);
                return 0;
            }
            if (sol[dmin[i][j]] == i)
                relax(dmin[i][j]);
        }

    return 0;
}