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

#define DIM 100010
using namespace std;

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

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;
}

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

    scanf ("%d %d", &N , &M );
    scanf ("%d %d", &st, &fi);

    for (int i = 1; i <= M; i ++)
    {
        scanf ("%d %d %d", &X, &Y, &Z);
        List[X].push_back(make_pair(Y, Z));
    }

    int l = 1, r = 4, mid;
    while (l <= r)
    {
        mid = l + ((r - l) >> 1);
        memset (Marked, 0, sizeof(Marked));

        DFS (st, mid);

        if (Marked[fi])
            r = mid - 1;
        else
            l = mid + 1;
    }

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

    fclose (stdin );
    fclose (stdout);

    return 0;
}