#include <stdio.h>
#include <vector>
#include <queue>

#define INF 1000000000

#define MAX 30001

struct Andrei {
    int val, cost;
};

std::vector< Andrei > noduri[ MAX + 1 ];

int n, m, X, Y;

bool ok[ MAX + 1 ];
int dp[ MAX + 1 ];
std::queue<int> q;
void Lee() {
    for( int i = 0; i <= n; i++ )
        dp[ i ] = INF;
    
    dp[ X ] = 0;
    ok[ X ] = 1;
    q.push( X );
    while( !q.empty() ) {
        int nod = q.front();
        q.pop();

        int Cost;
        ok[ nod ] = 1;
        int right = noduri[ nod ].size();
        for( int i = 0; i < right; i++ ) {
            if( nod < noduri[ nod ][ i ].val )
                Cost = noduri[ nod ][ i ].cost;
            else Cost = -noduri[ nod ][ i ].cost;
            if( !ok[ noduri[ nod ][ i ].val ] && dp[ noduri[ nod ][ i ].val ] > dp[ nod ] + Cost ) {
                dp[ noduri[ nod ][ i ].val ] = dp[ nod ] + Cost;
                ok[ noduri[ nod ][ i ].val ] = 1;
                q.push( noduri[ nod ][ i ].val );
               //  printf( "cost =  %d pt noul %d de la nodul %d\n", dp[ noduri[ nod ][ i ].val ], noduri[ nod ][ i ].val, nod );
            }
        }
    }

}

int main()
{
    FILE *fin = fopen( "sate.in", "r" );
    fscanf( fin, "%d %d %d %d", &n, &m, &X, &Y );

    int x, y, cost;
    for( int i = 0; i < m; i++ ) {
        fscanf( fin, "%d %d %d", &x, &y, &cost );
        noduri[ x ].push_back( { y, cost } );
        noduri[ y ].push_back( { x, cost } );
    }
    fclose( fin );

    Lee();

    FILE *fout = fopen( "sate.out", "w" );
    fprintf( fout, "%d\n", dp[ Y ] );
    fclose( fout );
    return 0;
}