#include <vector>
//#include <queue>
#include <fstream>
#include <utility>
#include <iostream>
#define NMAX 30020
using namespace std;

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

vector<pair<int, int> >v[NMAX];
//queue<int>coada;
bool p[NMAX];
int n, m, x, y;

int main()
{

    fin >> n >> m >> x >> y;
    int a, b, d;
    for (int i = 1; i <= m; ++i)
    {
        fin >> a >> b >> d;
        v[a].push_back(make_pair(b, d));
        //v[b].push_back(make_pair(a, d));
    }
   // coada.push(x);
    p[x] = 1;
    int nod, rs=0,cur;
    cur=x;
    while (1)
    {
        nod = cur;
        if (nod == y)
        {
            break;
        }
        //   cout << nod << "\n";
        for (int i = 0; i < sizeof(v[nod]); ++i)
        {
            if (!p[v[nod][i].first])
            {
                if (v[nod][i].first > nod)
                {
                    rs += v[nod][i].second;
                }
                else
                {
                    rs -= v[nod][i].second;
                }
                p[v[nod][i].first] = 1;
                //coada.push(v[nod][i].first);
                cur=v[nod][i].first;
                break;
            }
        }
       // coada.pop();
    }
    fout << rs;
    return 0;
}