#include <iostream>
#include <vector>

class Edge {
public:
    int begin;
    int end;
    int weight;
    Edge(int begin, int end, int weight) : begin(begin), end(end), weight(weight){
    }
};
class Graph {
private:
    std::vector<Edge> edges;
    int size;
public:
    Graph (int size, std::vector<Edge> & edges) : edges(edges), size(size) {
    }
    int CountDistanceLessThanK (int start, int end, int k) {
        std::vector<int> result(size, 100000005);
        std::vector<int> currentres (size, 1000000005);
        result[start] = 0;
        currentres[start] = 0;
        for (int i = 0; i < k ; i++) {
            for (int j = 0; j < edges.size(); j++) {
                if(currentres[edges[j].end] > result[edges[j].begin] + edges[j].weight) {
                    currentres[edges[j].end] = result[edges[j].begin] + edges[j].weight;
                }
            }
            result = currentres;
        }
        return (result[end] < 100000005) ? result[end] : -1;
    }
};
int main() {
    std::vector<Edge> data;
    int N, M, K, S, F, S0, F0, P0;
    std::cin >> N >> M >> K >> S >> F;
    for (int i = 0; i < M; i++) {
        std::cin >> S0 >> F0 >> P0;
        Edge newe(S0-1, F0-1, P0);
        data.push_back(newe);
    }
    Graph graph(N, data);
    std::cout << graph.CountDistanceLessThanK(S-1, F-1, K);
    return 0;
}