#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <cmath>
#include <queue>
using namespace std;
template <class T> void checkmin(T &t,T x) {if(x < t) t = x;}
template <class T> void checkmax(T &t,T x) {if(x > t) t = x;}
template <class T> void _checkmin(T &t,T x) {if(t==-1) t = x; if(x < t) t = x;}
template <class T> void _checkmax(T &t,T x) {if(t==-1) t = x; if(x > t) t = x;}
typedef pair <int,int> PII;
typedef pair <double,double> PDD;
typedef long long ll;
#define foreach(it,v) for(__typeof((v).begin()) it = (v).begin(); it != (v).end ; it ++)
const int N = 1001;
#define inf (1<<29)
struct nod{int x,val;nod() {}friend bool operator < (const nod& a,const nod& b){return b.val<a.val;}
};
vector<struct nod> g[N],r[N];
priority_queue<nod,vector<nod> > Q;
int n,m,S,T,K,dist[N],out[N],size;
void dijkstra(){bool vi[N];vector<struct nod>::iterator iter;for(int i=1;i<=n;i++){vi[i]=0;dist[i]=inf;}dist[T]=0;while(1){int k=-1;for(int i=1;i<=n;i++)if(!vi[i] && (k==-1 || dist[i]<dist[k])) k=i;if(k==-1) break;vi[k]=1;vector<struct nod>::iterator iter;for(iter=r[k].begin();iter!=r[k].end();iter++)if(!vi[(*iter).x] && dist[(*iter).x]>dist[k]+(*iter).val)dist[(*iter).x]=dist[k]+(*iter).val;}
}
int astar(){dijkstra();nod v;v.x=S;v.val=dist[S];Q.push(v);vector<struct nod>::iterator iter;for(int i=0;i<=n;i++) out[i]=0;while(!Q.empty() && out[T]<K){v=Q.top();Q.pop();if(out[v.x]>=K) continue;if(v.x==T){out[v.x]++;if(v.x==T && out[v.x]==K) return v.val;}for(iter=g[v.x].begin();iter!=g[v.x].end();iter++){if(out[(*iter).x]>=K) continue;nod tmp;tmp.val=v.val-dist[v.x]+(*iter).val+dist[(*iter).x];tmp.x=(*iter).x;Q.push(tmp);}}return -1;
}
int main(){while(~scanf("%d%d",&n,&m)){int a,b,w;for(int i=1;i<=n;i++) { g[i].clear();r[i].clear(); }while(m--){scanf("%d%d%d",&a,&b,&w);nod tmp;tmp.x=b;tmp.val=w;g[a].push_back(tmp);tmp.x=a;r[b].push_back(tmp);}scanf("%d%d%d",&S,&T,&K);if(S==T) K++;int ans=astar();printf("%d\n",ans);}return 0;
}