#include <bits/stdc++.h>
using namespace std;
inline void read(int &x) {
    x = 0;
    char c = getchar();

    for (; c < '0' || c > '9'; c = getchar());

    for (; c >= '0' && c <= '9'; c = getchar())
        x = (x << 1) + (x << 3) + (c ^ 48);
}
const int N = 5e5 + 5, M = 1e6 + 5;
int n, m, s, t, w;
set<int> e[N];
int lin[N], nxt[M << 1], to[M << 1], tot;
void in(int x, int y) {
    nxt[++tot] = lin[x];
    lin[x] = tot;
    to[tot] = y;
}
int dis[N], fr[N];
bool vis[N];
priority_queue< pair<int, int>> q;
void dij() {
    memset(dis, 0x3f, sizeof dis);
    dis[s] = 0;
    q.push(make_pair(0, s));

    while (q.size()) {
        int x = q.top().second;
        q.pop();

        if (vis[x])
            continue;

        vis[x] = 1;

        for (int i = lin[x]; i; i = nxt[i]) {
            int y = to[i];

            if (dis[x] + 1 < dis[y]) {
                dis[y] = dis[x] + 1;
                fr[y] = x;

                if (!vis[y])
                    q.push(make_pair(-dis[y], y));
            }
        }
    }
}
int fa[N];
inline int get(int x) {
    return x == fa[x] ? x : (fa[x] = get(fa[x]));
}
int main() {
    freopen("road.in", "r", stdin);
    freopen("road.out", "w", stdout);
    read(n);
    read(m);

    for (int i = 1; i <= m; i++) {
        int x, y;
        read(x);
        read(y);
        read(w);
        in(x, y);
        in(y, x);
        e[x].insert(y);
        e[y].insert(x);
    }

    read(s);
    read(t);
    dij();

    if (dis[t] == 0x3f3f3f3f)
        return printf("-1\n"), 0;

    int p = t, q = fr[t];

    while (p != s) {
        e[p].erase(q);
        e[q].erase(p);
        p = q;
        q = fr[p];
    }

    for (int i = 1; i <= n; i++)
        fa[i] = i;

    for (int i = 1; i <= n; i++) {
        for (auto p = e[i].begin(); p != e[i].end(); ++p) {
            int x = get(i), y = get(*p);

            if (x != y)
                fa[y] = x;
        }
    }

    bool f = 1;

    for (int i = 1; i < n; i++)
        f &= (get(i) == get(i + 1));

    if (!f)
        printf("-1\n");
    else
        printf("%lld\n", 1ll * dis[t]*w);

    return 0;
}

请各位大佬指教！！！谢谢！！！