#include <iostream>
#include <queue>
#include <utility>
#include <functional>
#include <string.h>

using node = std::pair<int, int>;

int main()
{
        int n, m, x, y;
        scanf("%d %d %d %d", &n, &m, &x, &y);

        int *first = new int[n + 1]{};
        int *to = new int[m * 2 + 1];
        int *next = new int[m * 2 + 1];
        int *weight = new int[m * 2 + 1];
        int *visited = new int[n + 1]{};
        int *dist = new int[n + 1];
        int edge = 1;

        int a, b, c;
        for (int i = 0; i != m; ++i)
        {
                scanf("%d %d %d", &a, &b, &c);

                to[edge] = b;
                weight[edge] = c;
                next[edge] = first[a];
                first[a] = edge;
                ++edge;

                to[edge] = a;
                weight[edge] = c;
                next[edge] = first[b];
                first[b] = edge;
                ++edge;
        }

        memset(dist, -1, sizeof(*dist) * (n + 1));

        std::priority_queue<node, std::vector<node>, std::greater<node>> pq;
        int current, to_node;

        dist[x] = 0;
        pq.push(node{ 0, x });

        while (!pq.empty())
        {
                current = pq.top().second; pq.pop();

                if (current == y)
                        break;

                if (visited[current])
                        continue;

                visited[current] = 1;
                edge = first[current];
                while (edge)
                {
                        to_node = to[edge];
                        if (dist[to_node] == -1 || dist[to_node] > dist[current] + weight[edge])
                        {
                                dist[to_node] = dist[current] + weight[edge];
                                pq.push(node{ dist[to_node], to_node });
                        }
                        edge = next[edge];
                }
        }

        printf("%d\n", dist[y]);
}