#include <stdio.h>

#define FIN "pscnv.in"
#define FOUT "pscnv.out"
#define nmax 50001

struct nod {int vf, c;
            nod *next;};
nod *q;
typedef nod *pnod;
pnod a[nmax], liste[nmax];

int d[nmax], s[nmax], i, j, k, n, m, x, y, cost;
int nstart, min, poz, nfin;

void addmuchie (int x, int y, int cost)
{
  nod *p = new nod;
  p -> c = cost;
  p -> vf = y;
  p -> next = a[x];
  a[x] = p;
}

void add (int x, int y)
{
  nod *p = new nod;
  p -> vf = y;
  p -> next = liste[x];
  liste[x] = p;
}

int max (int x, int y)
{
  if (x < y)
    return y;
  return x;
}

int
 main ()
{
  freopen (FIN, "rt", stdin);
  freopen (FOUT, "wt", stdout);
  
  scanf ("%d%d%d%d", &n, &m, &nstart, &nfin);
  for (i = 1; i <= m; i++)
   {
     scanf ("%d%d%d", &x, &y, &cost);
     addmuchie (x, y, cost);
   }
  for (i = 1; i <= n; i++)
    if (i != nstart)
      d[i] = 20001;
  for (q = a[nstart]; q != NULL; q = q -> next)
   {
     d[q -> vf] = q -> c;
     add (q -> c, q -> vf);
   }
  s[nstart] = 1;
  for (k = 1; k < n; k++)
   {
     min = 0;
     for (i = 1; i <= 1000; i++)
      { if (liste[i] != NULL)
          for (q = liste[i]; q != NULL; q = q -> next)
            if (d[q -> vf] == i && s[q -> vf] != 1)
             {
               min = i;
               poz = q -> vf;
               break;
             }
        if (min == i)
          break;
      }
     s[poz] = 1;
     for (q = a[poz]; q != NULL; q = q -> next)
       if (d[q -> vf] > max (min, q -> c))
        {
          d[q -> vf] = max (min, q -> c);
          add (max(min, q -> c), q -> vf);
        }
   }
  printf ("%d\n", d[nfin]);
  return 0;
}