using System;
// using System.Security.AccessControl;
using Newtonsoft.Json; // JsonConvert
// using Newtonsoft.Json.Linq; // JObject

namespace ConsoleAppDemoOne
{
    public static class ProgramOne
    {
        public static void Main(string[] args)
        {
            var nInput = Console.ReadLine();
            var flightsInput = Console.ReadLine();
            var srcInput = Console.ReadLine();
            var dstInput = Console.ReadLine();
            var kInput = Console.ReadLine();

            var n = Convert.ToInt32(nInput);
            var scr = Convert.ToInt32(srcInput);
            var dst = Convert.ToInt32(dstInput);
            var k = Convert.ToInt32(kInput);
            Console.WriteLine(n.GetType());
            
            // /*sing Newtonsoft.Json; // JsonConvert
            // using Newtonsoft.Json.Linq; // JObject*/
            // var flights = (JObject)JsonConvert.DeserializeObject(flightsInput);
            // Console.WriteLine(flights);
            // Console.WriteLine(flights.GetType());

            try
            {
                var flights = JsonConvert.DeserializeObject<int[][]>(flightsInput ?? string.Empty);
                Console.WriteLine(flights);
                if (flights == null) return;
                Console.WriteLine(flights.GetType());

                var sl = new Solution();
                Console.WriteLine(sl.FindCheapestPrice(n, flights, scr, dst, k));

                // Console.ReadKey();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex);
            }
        }
    }

    public class Solution
    {
        public int FindCheapestPrice(int n, int[][] flights, int src, int dst, int k)
        {
            const int inf = 10000 * 101 + 1;
            // int[,] f = new int[k + 2, n];
            var f = new int[k + 2, n];
            for (var i = 0; i < k + 2; ++i)
            {
                for (var j = 0; j < n; ++j)
                {
                    f[i, j] = inf;
                }
            }

            f[0, src] = 0;
            for (var t = 1; t <= k + 1; ++t)
            {
                foreach (var flight in flights)
                {
                    int j = flight[0], i = flight[1], cost = flight[2];
                    f[t, i] = Math.Min(f[t, i], f[t - 1, j] + cost);
                }
            }

            var ans = inf;
            for (var t = 1; t <= k + 1; ++t)
            {
                ans = Math.Min(ans, f[t, dst]);
            }

            return ans == inf ? -1 : ans;
        }
    }
    
}