#include<iostream>
#include<cstdlib>
#include<cstdio>
#include<queue>
#include<cmath>
#include<cstring> 

using namespace std;

const int maxedge=2200000;
const int maxnode=2100000;
int nodecount,edgecount,s,t,k;
int dis[maxnode],from[maxnode],to[maxnode],val[maxnode];
/////////////////////图信息 
struct edgenode{
	int to,dis,next;
}e[maxedge];
int head[maxnode],tot;
void edge(int u,int v,int w)
{
	e[++tot].to=v;
	e[tot].dis=w;
	e[tot].next=head[u];
	head[u]=tot;
}
///////////////邻接表
struct Node{
	int num,dist;
	int g,h;
	Node(int x,int y){
		num=x;dist=y;
	}
	Node(int x,int y,int z){
		num=x,g=y,h=z;
		dist=g+h;
	}
	bool operator < (const Node &x)const{
		return dist>x.dist;
	}
};
void dijkstra(int s)
{
	priority_queue<Node> que;
	memset(dis,127/3,sizeof(dis));
	dis[s]=0;
	que.push(Node(s,0));
	while(!que.empty()){
		Node node=que.top();que.pop();
		s=node.num;
		if(node.dist != dis[s]) continue;
		int x=head[s];
		while(x!=0){
			int to=e[x].to;
			if(dis[to]> dis[s]+e[x].dis){
				dis[to]=dis[s]+e[x].dis;
				que.push(Node(to,dis[to]));
			}
			x=e[x].next;
		}
	}
}
////////////////dijkstra
void clear()
{
	memset(head,0,sizeof(head));
	memset(e,0,sizeof(e));
	//for(int i=1;i<=tot;i++){
	//	cout<<e[i].next<<e[i].dis<<e[i].to;
//	}
	tot=0;
}
void secondedge()
{
	for(int i=1;i<=edgecount;i++)
		edge(from[i],to[i],val[i]);
}
int Astar(int s,int t,int k)
{
	if(s==t) k++;
	dijkstra(t);
	priority_queue<Node>q;
	clear();
	secondedge();
	q.push(Node(s,0,dis[s]));
	while(!q.empty()){
		Node x=q.top();q.pop();
		if(x.num==t){
			k--;
			if(k==0){
				return x.g;
			}
		}
		int xx=head[x.num];
		while(xx!=0){
			q.push(Node( e[xx].to , x.g+e[xx].dis , dis[e[xx].to] ));
			xx=e[xx].next;
		}
	}
	return -1;
}
///////////////////Astar
int main()
{
	//freopen("cowjog.in","r",stdin);
   // freopen("cowjog.out","w",stdout);
	scanf("%d%d",&nodecount,&edgecount);
	for(int i=1;i<=edgecount;i++){
		scanf("%d%d%d",&from[i],&to[i],&val[i]);
		edge(to[i],from[i],val[i]);
	}
	scanf("%d%d%d",&s,&t,&k);
	printf("%d",Astar(s,t,k));
	return 0;
}