#include <iostream>

#include <cstdio>

#include <cstdlib>

#include <cstring>

#include <cmath>

#include <queue>

#include <map>

#include <set>

#include <string>

#include <vector>

#define LL long long

using namespace std;

const int maxN = ;

//链式前向星

struct Edge

{

    int to, next;

    int val;

}edge[maxN*];

int head[maxN], cnt;

void addEdge(int u, int v, int val)

{

    edge[cnt].to = v;

    edge[cnt].next = head[u];

    edge[cnt].val = val;

    head[u] = cnt;

    cnt++;

}

void initEdge()

{

    memset(head, -, sizeof(head));

    cnt = ;

}

int n, m, k, to;

LL dis[maxN];

void input()

{

    initEdge();

    memset(dis, -, sizeof(dis));

    int u, v, t;

    for (int i = ; i <= m; ++i)

    {

        scanf("%d%d%d", &u, &v, &t);

        addEdge(u, v, t);

        addEdge(v, u, t);

    }

}

inline LL myMax(LL x, LL y)

{

    return x > y ? x : y;

}

struct Item

{

    int index;

    LL val;

    int step;

};

void work()

{

    int u, v, t, step;

    LL val, len;

    Item p, tmp;

    queue<Item> q;

    dis[]= ;

    p.index = ;

    p.step = ;

    p.val = ;

    q.push(p);

    while (!q.empty())

    {

        p = q.front();

        q.pop();

        u = p.index;

        step = p.step;

        val = p.val;

        for (int i = head[u]; i != -; i = edge[i].next)

        {

            v = edge[i].to;

            len = edge[i].val;

            if (dis[v] == - || myMax(val, len) < dis[v])

            {

                dis[v] = myMax(val, len);

                p.index = v;

                p.step = step+;

                p.val = dis[v];

                if (p.step < k)

                    q.push(p);

            }

        }

    }

    cout << dis[to] << endl;

}

int main()

{

    //freopen("test.in", "r", stdin);

    //freopen("test.out", "w", stdout);

    while (scanf("%d%d%d%d", &n, &m, &k, &to) != EOF)

    {

        input();

        work();

    }

    return ;

}