#include <bits/stdc++.h>

using namespace std;

ifstream f("sate.in");
ofstream g("sate.out");

vector<pair<int,int>>adj[100001];
queue<int>q;
int viz[100001];

int main()
{
    int n,m,start,stop,j,i,p,c,total = 0,x,y;
    f >> n >> m >> start >> stop;
    for(i = 1; i <= m; i++)
    {
        f >> x >> y >> c;
        adj[x].push_back({y,c});
        adj[y].push_back({x,c});
    }
    q.push(start);
    viz[start] = 1;
    while(!q.empty())
    {
        int nod_curent = q.front();
        viz[nod_curent] = 1;
        q.pop();
        for(i = 0; i < adj[nod_curent].size(); i++)
        {
            int vecin = adj[nod_curent][i].first;
            if(viz[vecin] == 0)
            {
                viz[vecin] = 1;
                if(vecin > nod_curent)
                    total = total + adj[nod_curent][i].second;
                else
                    total = total - adj[nod_curent][i].second;
                q.push(vecin);
            }
            if(vecin == stop)
            {
                g << total;
                return 0;
            }
        }
    }
    //g << total;
    return 0;
}