#include <bits/stdc++.h>
using namespace std;

const int N = 1e5 + 10;//无向图数组开双倍
const long long INF = 1e18; // 定义一个较大的常数用于初始化距离
typedef pair<long long, pair<int, int>> PII; // {距离, {节点, 免费次数}}

int h[N], ne[N], e[N], w[N], idx;
long long minCostWithFreeFlights[N][15];  // minCostWithFreeFlights[x][op] 表示到 x 点用 op 次免费航线的最小花费
int n, m, k;

void add(int a, int b, int c) 
{
    e[idx] = b, w[idx] = c;
    ne[idx] = h[a];
    h[a] = idx++;
}

long long dijkstra(int s, int t) 
{
    for (int i = 0; i < N; i++) 
        for (int j = 0; j <= k; j++) 
            minCostWithFreeFlights[i][j] = INF;

    priority_queue<PII, vector<PII>, greater<PII>> heap;
    minCostWithFreeFlights[s][0] = 0;
    heap.push({0, {s, 0}}); // {距离, {节点, 免费次数}}

    while (!heap.empty()) 
    {
        auto t = heap.top();
        heap.pop();

        long long d = t.first;
        int ver = t.second.first;
        int freeCount = t.second.second;

        if (d != minCostWithFreeFlights[ver][freeCount]) continue;  // 已更新的点跳过

        for(int i=h[ver];i!=-1;i=ne[i])
        {
            int j=e[i];
            int cost=w[i];

            // 不使用免费航线
            if(minCostWithFreeFlights[j][freeCount] > minCostWithFreeFlights[ver][freeCount] + cost)
            {
                minCostWithFreeFlights[j][freeCount] = minCostWithFreeFlights[ver][freeCount] + cost;
                heap.push({minCostWithFreeFlights[j][freeCount], {j, freeCount}});
            } 

            // 使用免费航线
            if(freeCount < k && minCostWithFreeFlights[j][freeCount + 1] > minCostWithFreeFlights[ver][freeCount])
            {
                minCostWithFreeFlights[j][freeCount + 1] = minCostWithFreeFlights[ver][freeCount];
                heap.push({minCostWithFreeFlights[j][freeCount + 1], {j, freeCount + 1}});
            }
        }
    }

    // 从 `minCostWithFreeFlights[t][0]` 到 `minCostWithFreeFlights[t][k]` 找到最小值，即最少花费
    long long minCost = INF;
    for (int i = 0; i <= k; i++) {
        minCost = min(minCost, minCostWithFreeFlights[t][i]);
    }
    return minCost;
}

int main() {
    ios::sync_with_stdio(0),cin.tie(0),cout.tie(0); 
    memset(h, -1, sizeof h);

    cin >> n >> m >> k;

    int s, t;
    cin >> s >> t;

    for (int i = 1; i <= m; i++) 
    {
        int a, b, c;
        cin >> a >> b >> c;
        add(a, b, c);
        add(b, a, c);
    }

    long long result = dijkstra(s, t);
    if (result == INF) 
        cout << -1 << endl; 
    else 
        cout << result << endl;

    return 0;
}