#include <cstdio>
#include <vector>
#define nmax 30005
FILE *f,*g;
using namespace std;

int n, m, X, Y, ans, SEM;

int VIZ[nmax];
vector < pair <int, int> > L[nmax];

void depth_first(int nod, int from, int cost)
{
    VIZ[nod] = 1;
    if (nod == Y)
    {
        ans = cost;
        SEM = 1;
    }
    for (int i = 0 ; i < L[nod].size() && !SEM ; i++)
    {
        int next = L[nod][i].first;
        if (from != next && !VIZ[next])
            depth_first(next, nod, cost + L[nod][i].second);
    }
}

int main()
{
    f=fopen("sate.in","r");
    g=fopen("sate.out","w");
    fscanf(f,"%d %d %d %d",&n,&m,&X,&Y);
    for(int i=1 ; i<=m ; i++)
    {
        int a, b, c;
        fscanf(f,"%d %d %d",&a,&b,&c);
        L[a].push_back (make_pair (b, c));
        L[b].push_back (make_pair (a, -c));
    }
    depth_first(X, 0, 0);
    fprintf(g,"%d\n",ans);
    return 0;
}