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

using namespace std;

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

const int NMAX= 30000;

struct GRAF
{
    int vf, cost;
};

vector <GRAF> d[NMAX+1];
queue <GRAF> q;
GRAF nr;

bool viz[NMAX+1];

int D[NMAX+1];

int main()
{
    int N, M, X, S, a, b, c;

    in >> N >> M >> X >> S;

    if( X>S )
    {
        int ff= X;
        X= S;
        S= ff;
    }

    for( int i= 1; i<=M; ++i )
    {
        in >> a >> b >> c;
        nr.vf= b;
        nr.cost= c;
        d[a].push_back( nr );
        nr.vf= a;
        d[b].push_back( nr );

    }

    //init
    nr.vf= X;
    nr.cost= 0;
    D[ X ]= 0;
    viz[X]= 1;
    //init

    //DFS
    int x, xcost;
    q.push(nr);
    while( !q.empty() )
    {
        GRAF aux= q.front();
        int lg= (int)d[aux.vf].size();
        for( int i= 0; i<lg; ++i )
        {
            x= d[aux.vf][i].vf;
            xcost= d[aux.vf][i].cost;

            if( viz[x]==0 )
            {
                if( aux.vf < x )
                {
                    D[x]= D[aux.vf] + xcost;
                }
                else D[x]= D[aux.vf] - xcost;

                q.push( d[aux.vf][i] );
                viz[x]= 1;
            }
        }
        q.pop();
    }
    //DFS

    out << D[S] << '\n';

    return 0;
}