UVA_10740

#include <iostream>
#include <bits/stdc++.h>
#define maxn 1005
#define inf 1000009
using namespace std;
typedef pair<int,int> ii;
typedef pair<long long int,int> li;
vector<ii> G[maxn];
vector<int> d[maxn];
int n,k;
int viscnt[maxn];
vector<int> res;
int dijkstra(int s,int d)
{
    res.clear();
    priority_queue<li,vector<li>,greater<li> > pq;
    pq.push({0,s});
    while(!pq.empty())
    {

        int u = pq.top().second,scoreu = pq.top().first;
        pq.pop();
        if(viscnt[u]>=k+1)
            continue;
        ++viscnt[u];
        if(u == d)
            res.push_back(scoreu);
        for(int i=0;i<G[u].size();++i)
        {
            int scorenow = scoreu+G[u][i].second,v=G[u][i].first;
            pq.push({scorenow,v});
        }

    }
    sort(res.begin(),res.end());
    if(res.size() < k)
        return -1;
    return res[k-1];


}
int main()
{
    //freopen("in.txt","r",stdin);
    int m;
    while(cin>>n>>m && (n||m))
    {
        for(int i=1;i<=n;++i)
        {
            G[i].clear();
            viscnt[i] =0;
        }
        int s,d;
        cin>>s>>d>>k;
        while(m--)
        {
            int u,v,w;
            cin>>u>>v>>w;
            G[u].push_back({v,w});

        }
        cout<<dijkstra(s,d)<<endl;


    }



}