#include<fstream>
#include<stdlib.h>
#include<stdio.h>
#define nmax 30004
using namespace std;

ofstream fout("sate.out");
int i, j ,n , m , x, y, k ;
bool viz[nmax];
int *A[nmax] , *B[nmax];
struct nod{int inf; nod *urm;} ;
int c[nmax *100];

int dis[nmax];
int bfs(int x,int y)
{
    int i, j;
  int p = 1;
  int u = 1;

    viz[x] = true;
 c[1] = x;
//    q = new nod;
//    q -> inf = x;
//    q -> urm = NULL;
//    p = u = q;
    while(p <= u &&dis[y] == 0)
    {
       // x = p -> inf;
        x = c[p];

        //fout << p -> inf <<" " ;
        for(i = 1; i <= A[x][0] ; i ++)
        {
            if(viz[A[x][i]] == false  )
            {
                viz[A[x][i]] = true;
                c[++u] = A[x][i];
                if(x < A[x][i])
                dis[A[x][i]] = dis[x] + B[x][i ]    ;
                    else
                  dis[A[x][i]] = dis[x] - B[x][i ];





            }
        }
        ++p;
    }
    return dis[y] ;


}
void read()
{
    int i,j , d;
    scanf("%d %d %d %d", &n ,&m , &x, &y);

   for(i = 1; i <=n ;i++)
   {
       A[i] = (int *) malloc(sizeof(int) );
        B[i] = (int *) malloc( sizeof(int) );
        A[i][0] = B[i][0] = 0;
   }

    for(k = 1; k <= m ; k++)
    {
        scanf("%d %d %d",&i, &j, &d);

        A[i][0] ++;
        A[j][0] ++;
    }
    for(i = 1; i <= n ;i++)
    {
         A[i] = (int *) malloc((A[i][0] + 1) *sizeof(int));
         B[i] = (int *) malloc((A[i][0] + 1 ) *sizeof(int));
         A[i][0] = B[i][0] = 0;
    }


        fseek(stdin, 0, SEEK_SET);
    scanf("%d %d %d %d", &n ,&m , &x, &y);
    for(k =1; k <= m ;k++)
    {
        scanf("%d %d %d",&i, &j, &d);
        A[i][0]++;

        A[j][0]++;

        B[i][A[i][0]] = d;
        B[j][A[j][0]] = d;
        A[i][A[i][0]] = j;
        A[j][A[j][0]] = i;

    }
     fout << bfs(x,y);


   // fout<< dis[i] <<" " ;

}
int main()
{
    freopen("sate.in", "r", stdin);
    read();
    fclose(stdin);
    return 0;
}