#include<iostream>
#include<stdio.h>
#include<string.h>
#include<fstream>
#include<stdlib.h>

using namespace std;

const int LGMAX = int(3e4)+5;
int viz[LGMAX], Q[LGMAX*2],
    n,m,X,Y;
typedef struct nod
    {
        int inf,d;
        nod *urm;
    } TNOD;
TNOD *v[LGMAX],*p;

void add( int a, int b, int ds )
{
    p = new TNOD;
    p->inf = a;
    p->d = ds;
    p->urm = v[b];
    v[b] = p;
}

void citire()
{
    int i,x,y,ds;
    ifstream in("sate.in");
    in>>n>>m>>X>>Y;
    for( i=1; i<=m; i++ )
        {
            in>>x>>y>>ds;
            add( x, y, -ds );
            add( y, x, ds );
        }
    if(X>Y)
        {
            int q = Y;
            Y = X;
            X = q;
        }
}
int dst[LGMAX];

int bfs()
{
    int fi=0,ls=0;
    Q[ls++] = X;
    memset(dst,-1,sizeof(dst));
    dst[X] = 0;
    while( fi<=ls )
    {
        for( p=v[Q[fi]]; p; p=p->urm )
            if( dst[p->inf]==-1 )
                dst[p->inf] = dst[Q[fi]] + p->d,
                Q[ls++] = p->inf;
        if(dst[Y]!=-1) return dst[Y];
        fi++;
    }
}

int main()
{
    freopen("sate.out","w",stdout);
    citire();
    cout<<bfs()<<endl;
    return 0;
}