#include<stdio.h>
#include<string.h>
#include<queue>
#include<algorithm>
using namespace std;
const int INF  = 0x3f3f3f3f;
const int maxn = 1024;
const int maxm = 100008;
struct EDGE{ int v, nxt, w; };
struct NODE{int pos, Cost, F;bool operator < (const NODE & rhs) const {//重载的时候注意符号if(this->F == rhs.F) return this->Cost > rhs.Cost;return this->F > rhs.F;};
};EDGE Edge[maxm];
EDGE REdge[maxm];
int Head[maxn], RHead[maxn];
int cnt, Rcnt;
int N;
void init()
{memset(Head, -1, sizeof(Head));memset(RHead, -1, sizeof(RHead));cnt = Rcnt = 0;
}void AddEdge(int from, int to, int weight)
{Edge[cnt].w = weight;Edge[cnt].v = to;Edge[cnt].nxt = Head[from];Head[from] = cnt++;
}void AddREdge(int from, int to, int weight)
{REdge[Rcnt].w = weight;REdge[Rcnt].v = to;REdge[Rcnt].nxt = RHead[from];RHead[from] = Rcnt++;
}int vis[maxn];
int H[maxn];
void SPFA(int st)
{queue<int> que;memset(H, INF, sizeof(H));memset(vis, 0, sizeof(vis));H[st] = 0;que.push(st);while(!que.empty()){int cur = que.front(); que.pop();vis[cur] = 0;for(int i=RHead[cur]; i!=-1; i=REdge[i].nxt) {int v = REdge[i].v;if(H[v] > H[cur] + REdge[i].w) {H[v] = H[cur] + REdge[i].w;if(!vis[v]) {vis[v] = 1;que.push(v);}}}}
}int A_Star(int s, int t, int k)
{if(s == t) k++;if(H[s]==INF) return -1;priority_queue<NODE> que;NODE cur, into;cur.pos = s;cur.Cost = 0;cur.F = H[s];que.push(cur);int CNT = 0;while(!que.empty()){cur = que.top();que.pop();if(cur.pos == t) CNT++;if(CNT == k) return cur.Cost;for(int i=Head[cur.pos]; i!=-1; i=Edge[i].nxt){into.Cost = cur.Cost+Edge[i].w;into.F = cur.Cost+Edge[i].w+H[Edge[i].v];into.pos = Edge[i].v;que.push(into);}}return -1;
}int main(void)
{int M, K, S, des;while(~scanf("%d %d", &N, &M)){init();int from, to, weight;while(M--){scanf("%d %d %d",&from, &to, &weight);AddEdge(from, to, weight);AddREdge(to, from, weight);//建反向边
        }scanf("%d %d %d", &S, &des, &K);SPFA(des);//求其他点到终点的最短路，作为H值printf("%d\n", A_Star(S,des,K));}return 0;
}