#include <fstream>
using namespace std;

#define in "pscnv.in"
#define out "pscnv.out"
#define NMAX 25010
#define INF 30001

#define ALB 0
#define GRI 1
#define NEGRU 2

typedef long int LI;
typedef struct nod {
        LI vf;
        LI cost;
        nod* next;
} *PNOD, NOD;

PNOD L[NMAX];

LI n, nod_p, nod_s, d[NMAX], color[NMAX], q[NMAX], m;
LI prim, ultim;
void BF(LI,LI);
void Read();
void Add(LI,LI,LI);
void Solve();

FILE *fout = fopen( out, "w" );

int main()
{
    Read();
    Solve();
    
    fclose( fout );
    return 0;
}

void Read()
{
     FILE *fin = fopen( in, "r" );
     fscanf( fin, "%ld%ld%ld%ld", &n, &m, &nod_p, &nod_s );
     LI v1, v2, cost;
     LI i;
     for ( i = 1; i <= m; ++i )
     {
         fscanf( fin, "%ld%ld%ld", &v1, &v2, &cost );
         Add(v1,v2,cost);
         d[v1] = d[v2] = INF;
     }
     fclose( fin );
}

void Add(LI i, LI j, LI cost )
{
     PNOD p = new NOD;
     p->vf = j;
     p->cost = cost;
     p->next = L[i];
     L[i] = p;
}

void BF( LI nod, LI limita )
{
     color[nod] = GRI;
     prim = ultim = 1;
     q[ultim] = nod;
     
     d[nod] = 0;
     
     PNOD j;
     LI i;
     while ( prim <= ultim )
     {
           i = q[prim];
           for ( j = L[i]; j; j = j->next )
               if ( color[j->vf] != NEGRU && j->cost <= limita )
               {
                    color[j->vf] = GRI;
                    ultim++;
                    q[ultim] = j->vf;
                    d[j->vf] = d[i] + 1;
               }
           prim++;
           color[i] = NEGRU;
     }
}

void Solve()
{
     LI k, i;
     for ( k = 1; k; ++k )
     {
         for ( i = 1; i <= n; ++i ) 
         {
             d[i] = INF;
             color[i] = ALB; 
         }
         
         BF ( nod_p, k );
         if ( d[nod_s] != INF ) 
         {
              fprintf( fout, "%ld\n", k );
              break;
         }
     }
}