#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> PII;
typedef pair<int, PII> PIII;
const int N = 1010, M = 2e5 + 10;
int n, m;
int s, t, k;
int h[N], rh[N], e[M], ne[M], w[M], idx;
int dist[N];
bool st[N];
int cnt[N];

void add(int h[], int a, int b, int c)
{
    e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx ++;
}
//预估函数f()
void dijkstra()
{
    memset(dist, 0x3f, sizeof dist);
    memset(st, 0, sizeof st);
    priority_queue<PII, vector<PII>, greater<PII>> heap;
    dist[t] = 0;
    heap.push({0, t});

    while (heap.size())
    {
        PII temp = heap.top();
        heap.pop();
        int distance = temp.first, id = temp.second;
        if (st[id]) continue;
        st[id] = true;

        for (int i = rh[id]; ~i; i = ne[i])
        {
            int j = e[i];
            if (dist[j] > distance + w[i])
            {
                dist[j] = distance + w[i];
                heap.push({dist[j], j});
            }
        }
    }
}

int astra()
{
    priority_queue<PIII, vector<PIII>, greater<PIII>> heap;
    heap.push({dist[s], {0, s}});

    while (heap.size())
    {
        PIII temp = heap.top();
        heap.pop();
        int distance = temp.second.first, id = temp.second.second;
        cnt[id] ++;
        if (cnt[t] == k) return distance;
        for (int i = h[id]; ~i; i = ne[i])
        {
            int j = e[i];
            if (cnt[j] < k)
            {
                heap.push({w[i] + distance + dist[j], {distance + w[i], j}});
            }
        }
    }
    return -1;
}

int main(void)
{
    memset(h, -1, sizeof h);
    memset(rh, -1, sizeof rh);
    cin >> n >> m;
    for (int i = 0; i < m; i ++)
    {
        int a, b, c;
        cin >> a >> b >> c;
        add(h, a, b, c);
        add(rh, b, a, c);
    }
    cin >> s >> t >> k;

    dijkstra();
    if (s == t) k ++;
    cout << astra() << endl;
    return 0;
}