#include <fstream>
#include <iostream>
#include <vector>
#include <queue>
#include <utility>

using namespace std;

ifstream fin ("sate.in");
ofstream fout ("sate.out");

struct data {int destNode, dist; };
vector < data > edge[30050];
int visited[30050], distanceLength[30050];

void BFS(int node)
{
    queue <int> NodeQ;
    visited[node] = 1;
    distanceLength[node] = 0;
    NodeQ.push(node);
    while (!NodeQ.empty())
    {
        node = NodeQ.front();
        for (int i = 0; i < edge[node].size(); ++i)
        {
            if (!visited[edge[node][i].destNode])
            {
                visited[edge[node][i].destNode] = 1;
                distanceLength[edge[node][i].destNode] = distanceLength[node] + edge[node][i].dist;
                NodeQ.push(edge[node][i].destNode);
            }
        }
        NodeQ.pop();
    }
}

int main()
{
    int n, m, x, y;
    int a, b, dist;
    data temp;
    fin >>n >>m >>x >>y;
    for (int i = 0; i < m; ++i)
    {
        fin >>a >>b >>dist;
        temp.destNode = b;
        temp.dist = dist;
        edge[a].push_back(temp);
        temp.destNode = a;
        temp.dist = -dist;
        edge[b].push_back(temp);
    }
    BFS(x);
    fout <<distanceLength[y];
    return 0;
}