#include <bits/stdc++.h>
#define cin ci
#define cout co
using namespace std;
ifstream cin("sate.in");
ofstream cout("sate.out");
const int INF = 1e9;
int n, m, x, y, start ,fin;
vector<vector<pair<int, int>>> graf;
vector<int> dist, viz;
priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> q;
void djisktra(int node)
{
    dist[node] = 0;
    q.push({0, node});
    while(!q.empty())
    {
        auto node = q.top().second;
        q.pop();
        if(!viz[node])
        {
            for(auto next:graf[node])
                if(dist[next.first] > dist[node] + next.second)
                {
                    dist[next.first] = dist[node] + next.second;
                    q.push({dist[next.first], next.first});
                }
            viz[node] = 1;
        }
    }
}
int main()
{
    cin >> n >> m >> start >> fin;
    graf.assign(n+1, vector<pair<int, int>>());
    dist.resize(n+1, INF);
    viz.resize(n+1);
    for(int i=1; i<=m; i++)
    {
        int z;
        cin >> x >> y >> z;
        if(x > y)
            swap(x, y);
        graf[x].push_back({y, z});
        graf[y].push_back({x, -z});
    }
    djisktra(start);
    cout << dist[fin];
    return 0;
}