#include <iostream>

#include <cstring>

#include <cstdlib>

#include <cstdio>

#include <queue>

#define MAXN 1005

#define MAXM 500005

#define INF 1000000000

using namespace std;

struct node

{

    int v, w, next;

}edge[MAXM], revedge[MAXM];

struct A

{

    int f, g, v;

    bool operator <(const A a)const {

        if(a.f == f) return a.g < g;

        return a.f < f;

    }

};

int e, vis[MAXN], d[MAXN], q[MAXM * ];

int head[MAXN], revhead[MAXN];

int n, m, s, t, k;

void init()

{

    e = ;

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

    memset(revhead, -, sizeof(revhead));

}

void insert(int x, int y, int w)

{

    edge[e].v = y;

    edge[e].w = w;

    edge[e].next = head[x];

    head[x] = e;

    revedge[e].v = x;

    revedge[e].w = w;

    revedge[e].next =revhead[y];

    revhead[y] = e++;

}

void spfa(int src)

{

    for(int i = ; i <= n; i++) d[i] = INF;

    memset(vis, , sizeof(vis));

    vis[src] = ;

    int h = , t = ;

    q[] = src;

    d[src] = ;

    while(h < t)

    {

        int u = q[h++];

        vis[u] = ;

        for(int i = revhead[u] ; i != -; i = revedge[i].next)

        {

            int v = revedge[i].v;

            int w = revedge[i].w;

            if(d[v] > d[u] + w)

            {

                d[v] = d[u] + w;

                if(!vis[v])

                {

                    q[t++] = v;

                    vis[v] = ;

                }

            }

        }

    }

}

int Astar(int src, int des)

{

    int cnt = ;

    priority_queue<A>Q;

    if(src == des) k++;

    if(d[src] == INF) return -;

    A t, tt;

    t.v = src, t.g = , t.f = t.g + d[src];

    Q.push(t);

    while(!Q.empty())

    {

        tt = Q.top();

        Q.pop();

        if(tt.v == des)

        {

            cnt++;

            if(cnt == k) return tt.g;

        }

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

        {

            t.v = edge[i].v;

            t.g = tt.g + edge[i].w;

            t.f = t.g + d[t.v];

            Q.push(t);

        }

    }

    return -;

}

int main()

{

    int x, y, w;

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

    {

        init();

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

        {

            scanf("%d%d%d", &x, &y, &w);

            insert(x, y, w);

        }

        scanf("%d%d%d", &s, &t, &k);

        spfa(t);

        printf("%d\n", Astar(s, t));

    }

    return ;

}