1 #include <iostream>
  2 #include <sstream>
  3 #include <ios>
  4 #include <iomanip>
  5 #include <functional>
  6 #include <algorithm>
  7 #include <vector>
  8 #include <string>
  9 #include <list>
 10 #include <queue>
 11 #include <deque>
 12 #include <stack>
 13 #include <set>
 14 #include <map>
 15 #include <cstdio>
 16 #include <cstdlib>
 17 #include <cmath>
 18 #include <cstring>
 19 #include <climits>
 20 #include <cctype>
 21 using namespace std;
 22 #define XINF INT_MAX
 23 #define INF 0x3FFFFFFF
 24 #define MP(X,Y) make_pair(X,Y)
 25 #define PB(X) push_back(X)
 26 #define REP(X,N) for(int X=0;X<N;X++)
 27 #define REP2(X,L,R) for(int X=L;X<=R;X++)
 28 #define DEP(X,R,L) for(int X=R;X>=L;X--)
 29 #define CLR(A,X) memset(A,X,sizeof(A))
 30 #define IT iterator
 31 typedef long long ll;
 32 typedef pair<int,int> PII;
 33 typedef vector<PII> VII;
 34 typedef vector<int> VI;
 35 int s ,t,k;
 36 const int maxn=1010;
 37 vector<PII>G[maxn];
 38 vector<PII>rG[maxn];
 39 int dis[maxn];
 40 int used[maxn];
 41 void init(int n)
 42 {
 43     memset(used,0,sizeof(used));
 44     for(int i=0;i<n;i++)
 45     {
 46         dis[i]=INF;
 47         G[i].clear();
 48         rG[i].clear();
 49     }
 50 }
 51 void add_edge(int u,int v,int w){
 52     G[u].push_back(make_pair(v,w));
 53     rG[v].push_back(make_pair(u,w));
 54 }
 55 void spfa()
 56 {
 57     queue<int>q;
 58     q.push(t);
 59     used[t]=1;
 60     dis[t]=0;
 61     while(!q.empty())
 62     {
 63         int u=q.front();
 64         for(int i=0;i<rG[u].size();i++)
 65         {
 66             int v=rG[u][i].first;
 67             int y=rG[u][i].second;
 68             if(dis[u]+y<dis[v])
 69             {
 70                 dis[v]=dis[u]+y;
 71                 if(!used[v])
 72                 {
 73                     used[v]=1;
 74                     q.push(v);
 75                 }
 76             }
 77         }
 78         q.pop();
 79         used[u]=0;
 80     }
 81 }
 82 int A_star()
 83 {
 84     priority_queue<pair<int,PII>,vector<pair<int,PII> >,greater<pair<int,PII> > >q;
 85     q.push(make_pair(dis[s],make_pair(0,s)));
 86     CLR(used,0);
 87     while(!q.empty())
 88     {
 89         pair<int,PII> p=q.top();
 90         q.pop();
 91         int f=p.first;
 92         int g=p.second.first;
 93         int u=p.second.second;
 94         used[u]++;
 95         if(used[t]==k)return f;
 96         if(used[u]>k)continue;
 97         for(int i=0;i<G[u].size();i++)
 98         {
 99             int v=G[u][i].first;
100             int d=G[u][i].second;
101             q.push(make_pair(g+dis[v]+d,make_pair(g+d,v)));
102         }
103     }
104     return -1;
105 }
106 int main()
107 {
108     ios::sync_with_stdio(false);
109     int n,m;
110     while(cin>>n>>m)
111     {
112         int u,v,w;
113         init(n);
114         for(int i=0;i<m;i++)
115         {
116             cin>>u>>v>>w;
117             add_edge(--u,--v,w);
118         }
119         cin>>s>>t>>k;
120         s--;t--;
121         spfa();
122         if(s==t)k++;
123         cout<<A_star()<<endl;
124     }
125     return 0;
126 }