// poj2499#include<algorithm>#include<iostream>#include<cstdlib>#include<cstring>#include<cstdio>#include<cmath>#include<queue>#define LL long long#define inf 2147483640#define Pi acos(-1.0)#define free(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);using namespace std;const int maxn=100010;struct edge {int to,next,w;}e[maxn<<1];int head[maxn],cnts[maxn],dis[maxn],vis[maxn];int n,m,S,T,K,cnt,U[maxn],V[maxn],W[maxn];struct data {	int num,w;	friend bool operator < (const data a,const data b) {		return a.w>b.w;	}};struct node {	int num,g,h;	friend bool operator < (const node a,const node b) {		return a.g+a.h>b.g+b.h;	}};void link(int u,int v,int w) {	e[++cnt]=(edge){v,head[u],w};head[u]=cnt;}void Dijkstra() {	for (int i=1;i<=n;i++) dis[i]=inf;dis[T]=0;	priority_queue<data> q;	data x=(data){T,0};q.push(x);	while (!q.empty()) {		x=q.top();q.pop();		if (vis[x.num]) continue;		vis[x.num]=1;		for (int i=head[x.num];i;i=e[i].next) if (dis[e[i].to]>x.w+e[i].w) {				dis[e[i].to]=e[i].w+x.w;				q.push((data){e[i].to,dis[e[i].to]});			}	}}int Astar() {	node x=(node){S,0,dis[S]};	priority_queue<node> q;q.push(x);	while (!q.empty()) {		x=q.top();q.pop();		cnts[x.num]++;		if (cnts[x.num]>K) continue;		if (cnts[T]==K) return x.g;		for (int i=head[x.num];i;i=e[i].next) q.push((node){e[i].to,x.g+e[i].w,dis[e[i].to]});	}	return -1;}int main() {	scanf("%d%d",&n,&m);	for (int i=1;i<=m;i++) {		scanf("%d%d%d",&U[i],&V[i],&W[i]);		link(V[i],U[i],W[i]);	}	scanf("%d%d%d",&S,&T,&K);	if (S==T) K++;	Dijkstra();	memset(head,0,sizeof(head));cnt=0;	for (int i=1;i<=m;i++) link(U[i],V[i],W[i]);	int ans=Astar();	printf("%d",ans);	return 0;}