/**
 * Code by Patrick Sava
 * "Spiru Haret" National College of Bucharest
 **/

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

using namespace std;

const int MAX = 3e4 + 14 ;

int dist [ MAX ] ;

queue < int > Q ;

vector < pair < int , int > > gr [ MAX ] ;

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

int main()
{
    int n , m , a , b ;
    cin >> n >> m >> a >> b ;
    while ( m -- ) {
        int x , y , cost ;
        cin >> x >> y >> cost ;
        gr [ x ].push_back ( make_pair ( y , cost ) ) ;
        gr [ y ].push_back ( make_pair ( x , -cost ) ) ;
    }
    for ( int i = 1 ; i <= n ; ++ i ) {
        dist [ i ] = 1 << 29 ;
    }
    dist [ a ] = 0 ;
    Q.push ( a ) ;
    while ( !Q.empty() )
    {
        int nod = Q.front() ;
        Q.pop() ;
        for ( auto x : gr [ nod ] ) {
            if ( dist [ x.first ] > dist [ nod ] + x.second ) {
                 dist [ x.first ] = dist [ nod ] + x.second ;
                 Q.push ( x.first ) ;
            }
        }
    }
    cout << dist [ b ] << '\n' ;
    return 0;
}