#include<cstdio>
#include<queue>
#include<cstring>
using namespace std;
struct sit
{
	int p,dis,val;
}s1,s2;
int first[1010],next[100010],length[100010],to[100010],f[1010],
first2[1010],next2[100010],to2[100010],time[1010];
bool b[1010];
struct cmp
{
	bool operator()(const sit &a,const sit &b)
	{
		return a.val>b.val;
	}
};
priority_queue<sit,vector<sit>,cmp> q;
int main()
{
	int i,j,k,l,m,n,p,x,y,z,s,t,min;
	scanf("%d%d",&n,&m);
	for (i=1;i<=m;i++)
	{
		scanf("%d%d%d",&x,&y,&z);
		next[i]=first[x];
		first[x]=i;
		length[i]=z;
		to[i]=y;
		next2[i]=first[y];
		first2[y]=i;
		to2[i]=x;
	}
	scanf("%d%d%d",&s,&t,&k);
	memset(f,0x42,sizeof(f));
	f[t]=0;
	for (i=1;i<=n;i++)
	{
		p=-1;
		min=0x7f7f7f7f;
		for (j=1;j<=n;j++)
		  if (f[j]<min&&!b[j])
		  {
		  	p=j;
		  	min=f[j];
		  }
		if (p==-1) break;
		b[p]=1;
		for (j=first2[p];j;j=next2[j])
		  if (f[to2[j]]>f[p]+length[j])
		    f[to2[j]]=f[p]+length[j];
	}
	s1.p=s;
	s1.dis=0;
	s1.val=f[s];
	q.push(s1);
	if(s==t) k++; 
	while (!q.empty())
	{
		s1=q.top();
		printf("p=%d dis=%d val=%d\n",s1.p,s1.dis,s1.val);
		q.pop();
		if (++time[s1.p]==k)
		{
			printf("%d\n",s1.val);
			return 0;
		}
		for (i=first[s1.p];i;i=next[i])
		{
	    	s2.p=to[i];
			s2.dis=s1.dis+length[i];
			s2.val=s2.dis+f[s2.p];
			q.push(s2);
		}
	}
	printf("-1\n");
}