#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <queue>
#define pb push_back
using namespace std;
const int maxn = 5e3 + 50;
int mincost[maxn][50+5];
bool inqueue[maxn][50+5];typedef struct Edge
{int target,cost;Edge(int target ,int cost){this->target = target , this->cost = cost;    }
};typedef struct status
{int pos,step;    status(int pos,int step){this->pos = pos , this->step = step;}
};queue<status>q;
vector<Edge>E[maxn];
int n,m,st,ed,k;void bfs()
{mincost[st][0] = 0;q.push(status(st,0));while(!q.empty()){int pos = q.front().pos , step = q.front().step ; q.pop();int thiscost = mincost[pos][step];inqueue[pos][step] = false;for(int i = 0 ; i < E[pos].size() ; ++ i){int nextnode = E[pos][i].target;int thisstep = min(52,step+1);if (mincost[nextnode][thisstep] == -1 || mincost[nextnode][thisstep] > thiscost + E[pos][i].cost){mincost[nextnode][thisstep] = thiscost + E[pos][i].cost;if (!inqueue[nextnode][thisstep]){q.push(status(nextnode,thisstep));inqueue[nextnode][thisstep] = true;}}}}
}int main(int argc,char *argv[])
{while(~scanf("%d%d",&n,&m)){memset(mincost,-1,sizeof(mincost));memset(inqueue,false,sizeof(inqueue));for(int i = 1 ; i <= m ; ++ i){int u,v,t;scanf("%d%d%d",&u,&v,&t);E[u].pb(Edge(v,t));E[v].pb(Edge(u,t));}scanf("%d%d%d",&st,&ed,&k);bfs();int ans = mincost[ed][k];for(int i = k + 1 ; i <= 52 ; ++ i)if (mincost[ed][i] != -1){if (ans == -1)ans = mincost[ed][i];ans = min (ans , mincost[ed][i]);}printf("%d\n",ans);for(int i = 1 ; i <= n ; ++ i)E[i].clear();}return 0;
}