t1995

import java.io.*;
import java.util.*;

public class t1995 {

    FastScanner in;
    PrintWriter out;

    class Edge{
        int v, u;
        long w;
        Edge(int v, int u, long w){
            this.v = v;
            this.u = u;
            this.w = w;
        }
    }

    private void solve() throws IOException {
        int n = in.nextInt(), m = in.nextInt();
        int k = in.nextInt(), s = in.nextInt() - 1, f = in.nextInt() - 1;
        Edge[] a = new Edge[m];
        for(int i = 0; i < m; i++){
            a[i] = new Edge(in.nextInt() - 1, in.nextInt() - 1, in.nextLong());
        }
        long[][] dist = new long[n][k + 1];
        for(int i = 0; i < n; i++){
            for(int j = 0; j < k + 1; j++){
                dist[i][j] = Integer.MAX_VALUE;
            }
        }
        dist[s][0] = 0;
        for(int i = 0; i < k; i++){
            for(Edge j : a){
                dist[j.u][i + 1] = Math.min(dist[j.u][i + 1], dist[j.u][i]);
                if(dist[j.u][i + 1] > dist[j.v][i] + j.w){
                    dist[j.u][i + 1] = dist[j.v][i] + j.w;
                }
            }
        }
        out.print(dist[f][k] >= Integer.MAX_VALUE ? -1 : dist[f][k]);

    }



    class FastScanner {
        StringTokenizer st;
        BufferedReader br;

        FastScanner(InputStream s) {
            br = new BufferedReader(new InputStreamReader(s));
        }

        String next() throws IOException {
            while (st == null || !st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
            return st.nextToken();
        }

        boolean hasNext() throws IOException {
            return br.ready() || (st != null && st.hasMoreTokens());
        }

        int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

        long nextLong() throws IOException {
            return Long.parseLong(next());
        }

        double nextDouble() throws IOException {
            return Double.parseDouble(next().replace(',', '.'));
        }

        boolean hasNextLine() throws IOException {
            return br.ready();
        }

        String nextLine() throws IOException {
            return br.readLine();
        }

    }

    private void run() throws IOException {
        in = new FastScanner(System.in); //new FileInputStream(".in");
        out = new PrintWriter(System.out);

        solve();
        out.flush();
        out.close();
    }


    public static void main(String[] args) throws IOException {
        new Main().run();

    }
}