#include <fstream>
#include <vector>
#define MAX_SATE 30001
using namespace std;

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

struct sat
{
    int id,d;
};

int n,m,x,y,dist=0;
char visited[MAX_SATE];
vector <sat> G[MAX_SATE];

void DF(int i)
{
    visited[i] = '1';
    for (int j=0;j<G[i].size();++j)
    {
        if(visited[G[i][j].id]!='1')
        {
            dist += G[i][j].d;
            DF(G[i][j].id);
        }
    }
}
int main()
{
    int i,j,d;
    fin>>n>>m>>x>>y;

    for(int k=0;k<m;++k)
    {
        fin>>i>>j>>d;

        sat p,q;
        p.id = i;
        p.d = -d;
        q.id = j;
        q.d = d;

        G[i].push_back(q);
        G[j].push_back(p);

    }

    DF(x);
    fout<<dist;

    return 0;
}