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

#define NMax 30010
#define INF 2000000000

using  namespace std;

ifstream f("sate.in");
ofstream g("sate.out");

int nodes, edges, d[NMax], bg, ed;
vector< pair<int, int> > G[NMax];
queue<int> Q;
bool mark[NMax];

void BFS()
{
    for (int i = 1; i <= nodes; i++)
        if (i != bg)
            d[i] = INF;

    Q.push(bg);

    while (!Q.empty()) {
        int crtNode = Q.front();
        Q.pop();

        for (vector< pair<int, int> >::iterator it = G[crtNode].begin(); it != G[crtNode].end(); it++) {
            if (!mark[it->first]) {
                mark[it->first] = true;
                Q.push(it->first);
            }

            if (d[it->first] > d[crtNode] + it->second)
                d[it->first] = d[crtNode] + it->second;
        }
    }
}

int main()
{

    f >> nodes >> edges >> bg >> ed;

    int n1, n2, c;
    for (int i = 1; i <= edges; i++) {
        f >> n1 >> n2 >> c;

        G[n1].push_back(make_pair(n2, c));
        G[n2].push_back(make_pair(n1, -c));
    }

    BFS();

    g << d[ed];

    return 0;
}