#include <cstring>
#include <iostream>
#include <algorithm>
#include <queue>

#define x first
#define y second

using namespace std;

typedef pair<int, int> PII;
typedef pair<int, PII> PIII;

const int N = 1010, M = 200010;

int n, m, S, T, K;
int h[N], rh[N], e[M], w[M], ne[M], idx;
int f[N], cnt[N];
bool st[N];

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

void dijkstra() {
    priority_queue<PII, vector<PII>, greater<PII>> heap;
    heap.push({0, T});

    memset(f, 0x3f, sizeof f);
    f[T] = 0;

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

        int ver = t.y;
        if (st[ver]) continue;
        st[ver] = true;

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

int astar() {
    priority_queue<PIII, vector<PIII>, greater<PIII>> heap;
    heap.push({f[S], {0, S}}); //按照估价函数排序

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

        int ver = t.y.y, distance = t.y.x;
        cnt[ver]++;
        if (cnt[T] == K) return distance;

        for (int i = h[ver]; ~i; i = ne[i]) {
            int j = e[i];
            if (cnt[j] < K)
                heap.push({distance + w[i] + f[j], {distance + w[i], j}});
                                //真实值 + 边的长度 + 估价函数（距离T的最短距离）
        }
    }

    return -1;
}

int main() {
    scanf("%d%d", &n, &m);
    memset(h, -1, sizeof h);
    memset(rh, -1, sizeof rh);

    for (int i = 0; i < m; i++) {
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        add(h, a, b, c);
        add(rh, b, a, c);
    }
    scanf("%d%d%d", &S, &T, &K);
    if (S == T) K++;

    dijkstra();
    printf("%d\n", astar());

    return 0;
}