#include <iostream>

 #include <cstring>

 #include <queue>

 using namespace std;

 #define MAX_V 10008

 #define MAX_E 200008

 int N, M, K, T;

 int f[MAX_V];

 bool v[MAX_V];

 int n[MAX_E];

 int w[MAX_E];

 int t[MAX_E];

 int max_w = ;;

 int min_w = ;

 bool check(int l) {

   queue<pair<int, int> > q;

   memset(v, , sizeof(v));

   q.push(pair<int, int>(, K));

   while (!q.empty()) {

     pair<int, int> p = q.front();

     q.pop();

     if (p.first == T && p.second >= )

       return true;

     if (p.second ==  || v[p.first])

       continue;

     v[p.first] = true;

     for (int i = f[p.first]; i != ; i = n[i]) {

       if (w[i] > l || v[t[i]])

         continue;

       q.push(pair<int, int>(t[i], p.second - ));

     }

   }

   return false;

 }

 int find(int l, int r) {

   int res = r;

   while (l <= r) {

     int m = (l + r) / ;

     if (check(m)) {

       res = m;

       r = m - ;

     }

     else

       l = m + ;

   }

   return res;

 }

 int main() {

   memset(n, , sizeof(n));

   scanf("%d%d%d%d", &N, &M, &K, &T);

   for (int i = , j = ; i < M; i++) {

     int a, b, c;

     scanf("%d%d%d", &a, &b, &c);

     min_w = min(min_w, c);

     max_w = max(max_w, c);

     j++;

     w[j] = c;

     t[j] = b;

     n[j] = f[a];

     f[a] = j;

     j++;

     w[j] = c;

     t[j] = a;

     n[j] = f[b];

     f[b] = j;

   }

   if (T == )

     printf("0\n");

   else

     printf("%d\n", find(min_w, max_w));

   return ;

 }