#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <queue>
#define MAXN 1005
#define MAXM 500005
#define INF 1000000000
using namespace std;
struct node
{
int v, w, next;
}edge[MAXM], revedge[MAXM];
struct A
{
int f, g, v;
bool operator <(const A a)const {
if(a.f == f) return a.g < g;
return a.f < f;
}
};
int e, vis[MAXN], d[MAXN], q[MAXM * ];
int head[MAXN], revhead[MAXN];
int n, m, s, t, k;
void init()
{
e = ;
memset(head, -, sizeof(head));
memset(revhead, -, sizeof(revhead));
}
void insert(int x, int y, int w)
{
edge[e].v = y;
edge[e].w = w;
edge[e].next = head[x];
head[x] = e;
revedge[e].v = x;
revedge[e].w = w;
revedge[e].next =revhead[y];
revhead[y] = e++;
}
void spfa(int src)
{
for(int i = ; i <= n; i++) d[i] = INF;
memset(vis, , sizeof(vis));
vis[src] = ;
int h = , t = ;
q[] = src;
d[src] = ;
while(h < t)
{
int u = q[h++];
vis[u] = ;
for(int i = revhead[u] ; i != -; i = revedge[i].next)
{
int v = revedge[i].v;
int w = revedge[i].w;
if(d[v] > d[u] + w)
{
d[v] = d[u] + w;
if(!vis[v])
{
q[t++] = v;
vis[v] = ;
}
}
}
}
}
int Astar(int src, int des)
{
int cnt = ;
priority_queue<A>Q;
if(src == des) k++;
if(d[src] == INF) return -;
A t, tt;
t.v = src, t.g = , t.f = t.g + d[src];
Q.push(t);
while(!Q.empty())
{
tt = Q.top();
Q.pop();
if(tt.v == des)
{
cnt++;
if(cnt == k) return tt.g;
}
for(int i = head[tt.v]; i != -; i = edge[i].next)
{
t.v = edge[i].v;
t.g = tt.g + edge[i].w;
t.f = t.g + d[t.v];
Q.push(t);
}
}
return -;
}
int main()
{
int x, y, w;
while(scanf("%d%d", &n, &m) != EOF)
{
init();
for(int i = ; i <= m; i++)
{
scanf("%d%d%d", &x, &y, &w);
insert(x, y, w);
}
scanf("%d%d%d", &s, &t, &k);
spfa(t);
printf("%d\n", Astar(s, t));
}
return ;
}
//K短路