#include <iostream>
#include <fstream>
#include <iostream>
using namespace std;
ifstream f("sate.in");
ofstream g("sate.out");
int n,m,j,x,y,a,b,v[3001][3001],c,dist;

bool viz[30001];

int bfs(int s)
{
    if (s==y)
        {   g << dist ;
            return 0;
        }
    viz[s]=1;
    for (int i=1;i<=n;++i)
        if (!viz[i] && v[s][i] != 0)
            {
                dist+=v[s][i];

                viz[i] = 1 ;
                bfs(i);
            }}
int main()
{
    f>>n>>m>>x>>y;
    for (int i=1;i<=m;++i)
    {
        f>>a>>b>>c;
        v[a][b]=c;
        v[b][a]=-c;
    }

   bfs(x) ;


    return 0;
}