#include <bits/stdc++.h>

#include <stdlib.h>

using namespace std;



ifstream fin("sate.in");

ofstream fout("sate.out");

struct drum

{

    int nod,cost;

} varaux1,varaux2;



int seen [40001];

int n,x,y,distanta;

vector<drum>v[100050];

void dfs ( int nod )

{

    if(nod==y)

    {

        fout<<distanta;

        exit(0);

    }

    seen[nod]=-1;

    for(int i=0; i<v[nod].size(); i++)

        if(seen[v[nod][i].nod]==0)

        {

            distanta+=v[nod][i].cost;

            dfs(v[nod][i].nod);

            distanta-=v[nod][i].cost;

        }

}







int main()

{

    int i,m,a,b,dist;

    fin>>n>>m>>x>>y;

    for(i=0; i<m; i++)

    {

        fin>>a>>b>>dist;

        varaux1= {b,dist};

        varaux2= {a,-dist};

        v[a].push_back(varaux1);

        v[b].push_back(varaux2);

    }

    dfs(x);

    return 0;

}