#include <cstdio>
#include <vector>
#include <bitset>
#include <cstring>
#include <algorithm>

#define DIM 256000
using namespace std;

int N, M, st, fi, X, Y, Z;
vector <pair <int, int> > List[DIM];
bitset <DIM> Marked;
char String[12];

void DFS (int nod, int cost)
{
    Marked[nod] = 1;

    vector <pair <int, int> > :: iterator i;
    for (i = List[nod].begin(); i != List[nod].end(); i ++)
    {
        pair <int, int> vec = *i;

        if(!Marked[vec.first] && vec.second <= cost)
            DFS(vec.first, cost);
    }

    return;
}

inline void read (int &value)
{
    value = 0;
    memset (String, 0, sizeof(String));
    scanf ("%s", String + 1);

    for (int i = 1; String[i]; i ++)
        value = value * 10 + (String[i] - '0');

    return;
}

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

    read  (N); read  (M);
    read (st); read (fi);

    for (int i = 1; i <= M; i ++)
    {
        read (X); read (Y); read (Z);
        List[X].push_back(make_pair(Y, Z));
    }

    int result = -1;
    for (int step = (1<<9); step; step >>= 1)
    {
        DFS (st, result + step);

        if (!Marked[fi])
            result += step;

        Marked.reset();
    }
    result ++;

    printf ("%d\n", result);

    fclose (stdin );
    fclose (stdout);

    return 0;
}