#include<queue>
#include<cstring>
#include<set>
#include<map>
#include<stack>
#include<string>
#include<cmath>
#include<vector>
#include<cstdio>
#include<iostream>
#include<algorithm>
typedef long long ll;
using namespace std;
const int maxn = 1000 + 10;
const int seed = 131;
const ll MOD = 1e9 + 7;
const int INF = 0x3f3f3f3f;
int n, m, k, tot;
struct Edge{int v, w, next;
}edge[maxn * 100];
struct As{int f, g, pos;bool operator < (const As a) const{return a.f == f? a.g < g : a.f < f;}
};
struct que{int u, v, w;
}q[100005];
int head[maxn], dis[maxn];
bool vis[maxn];
void init(){memset(head, -1, sizeof(head));tot = 0;
}
void addEdge(int u, int v, int w){edge[tot].v = v;edge[tot].w = w;edge[tot].next = head[u];head[u] = tot++;
}
void spfa(int st){for(int i = 0; i <= n; i++) dis[i] = INF;memset(vis, false, sizeof(vis));vis[st] = true;dis[st] = 0;queue<int> q;while(!q.empty()) q.pop();q.push(st);while(!q.empty()){int u = q.front();q.pop();vis[u] = false;for(int i = head[u]; i != -1; i = edge[i].next){int v = edge[i].v;int w = edge[i].w;if(dis[v] > dis[u] + w){dis[v] = dis[u] + w;if(!vis[v]){vis[v] = true;q.push(v);}}}}
}
int Astar(int st, int end){int cnt = 0;priority_queue<As> q;while(!q.empty()) q.pop();if(st == end) k++;if(dis[st] == INF) return -1;As a, b;a.pos = st, a.g = 0, a.f = a.g + dis[st];q.push(a);while(!q.empty()){a = q.top();q.pop();if(a.pos == end){cnt++;if(cnt == k) return a.f;}for(int i = head[a.pos]; i != -1; i = edge[i].next){b.pos = edge[i].v;b.g = a.g + edge[i].w;b.f = b.g + dis[b.pos];q.push(b);}}return -1;
}
int main(){while(~scanf("%d%d" ,&n, &m)){init();for(int i = 1; i <= m; i++){scanf("%d%d%d", &q[i].u, &q[i].v, &q[i].w);addEdge(q[i].v, q[i].u, q[i].w);}int s, t;scanf("%d%d%d", &s, &t, &k);spfa(t);init();for(int i = 1; i <= m; i++){addEdge(q[i].u, q[i].v, q[i].w);}printf("%d\n", Astar(s, t));}return 0;
}