#include <bits/stdc++.h>

using namespace std;

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

struct Muchie
{
    int x, y, cost;

};

int n, m, a,b;
int dist[30005];
int viz[400005];

vector <Muchie> lista[30005];

void DFS (int nod)
{
    viz[nod] = 1;
    for(Muchie i: lista[nod])
    {
        if (viz[i.y]==0)
        {
            if (nod < i.y)
                dist[i.y] = dist[nod] + i.cost;
            else
                dist[i.y] = dist[nod] - i.cost;
            DFS(i.y);
        }

    }

}

int main()
{
    fin>>n>>m>>a>>b;
    for (int i = 1; i <= m; i++)
    {
        int x, y, cost;
        fin >> x >> y >> cost;
        lista[x].push_back({x, y, cost});
        lista[y].push_back({y, x, cost});
    }

    int cost = 0;
   DFS(a);
   fout<<abs(dist[b]);
    return 0;
}