#include<fstream>
#include<stdlib.h>
#include<stdio.h>
#define nmax 30004
using namespace std;
ifstream fin("sate.in");
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;
    if(x>y)
        swap(x,y);
    viz[x] = true;
    c[1] = x;


    while(dis[y] == 0)
    {

        for(i = 1, x = c[p]; i <= A[x][0] ; i ++)
        {
            if(viz[A[x][i]] == false )
            {
                viz[c[++u] = A[x][i]] = true;


                    dis[A[x][i]] = dis[x] + B[x][i];

                if(dis[y])
                    return dis[y];


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


}
void read()
{
    int i,j , d;


   fin >> n >> m >> x >>y;
for(i = 1; i <= n ;i++)

{

A[i] = (int *) realloc(A[i], sizeof(int));

A[i][0] = 0;

B[i] = (int *) realloc(B[i], sizeof(int));

B[i][0] = 0;

}

for(k =1; k <= m ;k++)

{

    fin >> i >> j >>d;

    A[i][0]++;

    A[i] = (int *) realloc(A[i] , (A[i][0] + 1 ) * sizeof(int));

    B[i] = (int *) realloc(B[i] , (A[i][0] + 1 ) * sizeof(int));

    A[j][0] ++;

    A[j] = (int *) realloc(A[j],  (A[j][0] + 1) * sizeof(int));

    B[j] = (int *) realloc(B[j],  (A[j][0] + 1) * sizeof(int));

    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 << bfs(x,y);


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

}
int main()
{

    read();
   fin.close();
    return 0;
}