#include <iostream>

#include <cstdio>

#include <string.h>

#include <cstring>

#include <queue>

using namespace std;

const int N = 1e3+;

const int M = +;

typedef long long ll;

const ll INF = 1e15;

int n,m,head[N],rehead[N],tot;

struct node {

    int v,w,next;

}E[M],reE[M];

void init() {

    tot=;

    memset(head,,sizeof(head));

    memset(rehead,,sizeof(rehead));

}

void addEdge(int u,int v,int w) {

    ++tot;

    E[tot].next = head[u];

    head[u]=tot;

    E[tot].v = v;

    E[tot].w = w;

    reE[tot].next = rehead[v];

    rehead[v]=tot;

    reE[tot].v = u;

    reE[tot].w = w;

}

bool inq[N]; ll d[N];

queue<int>que;

void spfa(int src) {

    while(!que.empty())

        que.pop();

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

    memset(inq,,sizeof(inq));

    d[src]=;

    inq[src] = ;

    que.push(src);

    while(!que.empty()) {

        int now = que.front();

        que.pop();

        //if(vis[now]) continue;

        //vis[now]=1;

        inq[now] = ;

        for(int i=rehead[now]; i; i=reE[i].next) {

            int v = reE[i].v;

            int w = reE[i].w;

            if(d[v] > d[now] + w) {

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

                if(!inq[v])

                    que.push(v);

            }

        }

    }

}

struct A {

    int v;

    ll f,g;

    ///v是current点 f(v)=g(v)+h(v) g(v):st到v的估值, h(v):v到ed的估值

    bool operator<(const A other) const {

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

        return other.f < f;

    }

};

int Astar(int st,int ed,int k) {

    priority_queue<A> Q;

    if(st==ed) k++;

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

    int cnt = ;

    A t,tt;

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

    Q.push(t);

    while (!Q.empty()) {

        tt = Q.top(); Q.pop();

        int u=tt.v;

        if(u == ed) {

            cnt++;

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

        }

        for(int i=head[u]; i; i=E[i].next) {

            t.v = E[i].v;

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

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

            Q.push(t);

        }

    }

    return -;

}

int main () {

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

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

        init();

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

            int x,y,z; scanf("%d%d%d",&x,&y,&z);

            addEdge(x,y,z);

        }

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

        spfa(t);

        //for(int i=1;i<=n;i++) cout << d[i]<<endl;

        cout<<Astar(s,t,k)<<endl;

    }

    return ;

}