#include <stdio.h>
    
FILE *fin;
int poz, val;
char buff[ ( 1 << 15 ) ];
char nextChar() {
    if( poz == sizeof( buff ) ) {
        fread( buff, 1, sizeof( buff ), fin );
        poz = 0;
    }
 
    return buff[ poz++ ];
}
 
bool f[ 100 ];
int readInt() {
    int rez = 0, ch;
    while( !f[ ch = nextChar() ] );
    do
        rez = rez * 10 + ch - '0';
    while( f[ ch = nextChar() ] );
    
    return rez;
}

#include <vector>
#include <bitset>
#include <queue>
#define MAX 30001
 
struct pp {
    int val, cost;
};
 
std::vector<pp> noduri[ MAX + 1 ];
 
int n, m, X, Y;
 
std::bitset<MAX + 1> ok;
int dp[ MAX + 1 ];
std::queue<int> q;
void Lee() {
    const int INF = ( 1 << 30 );
    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 );
            }
        }
    }
 
}
 
int main()
{
    ////////////////////////////////////
    val = sizeof( buff );
    
    f[ '1' ] = f[ '2' ] = f[ '3' ] = f[ '4' ] = f[ '5' ] = 1;
    f[ '6' ] = f[ '7' ] = f[ '8' ] = f[ '9' ] = f[ '0' ] = 1;
    ////////////////////////////////////

    fin = fopen( "sate.in", "r" );
    fread( buff, 1, sizeof( buff ), fin );
    n = readInt();
    m = readInt();
    X = readInt();
    Y = readInt();
 
    int x, y, cost;
    for( int i = 0; i < m; i++ ) {
        x = readInt();
        y = readInt();
        cost = readInt();
        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;
}