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

using namespace std;

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

vector<pair<int,int>> v[30005];

int drum,y;

bool viz[100005];

void dfs(int idnod)
{
    if (idnod==y)
    {
        fout<<drum<<'\n';
        exit(0);
    }
    viz[idnod]=true;
    for (int i=0;i<v[idnod].size();i++)
    {
        if (viz[v[idnod][i].first]==false)
        {
            int aux=drum;
            //if (v[idnod][i].first>idnod)
                drum+=v[idnod][i].second;
            //else
                //drum-=v[idnod][i].second;
            dfs(v[idnod][i].first);
            drum=aux;
        }
    }
}

int main()
{
    int n,m,x,drum=0;
    fin>>n>>m>>x>>y;
    for (int i=0;i<m;i++)
    {
        int a,b,c;
        fin>>a>>b>>c;
        v[a].push_back(make_pair(b, c));
        v[b].push_back(make_pair(a, -c));
    }
    dfs(x);
    fout<<drum<<'\n';
    return 0;
}