#include <cstdio>
#include <vector>
#include <string>
 
using namespace std;
 
#define DIM2 1<<15
#define DIM 10000
void read();
void bfs();
vector <int>G[DIM2];
vector <int>Cost[DIM2];
char vec[DIM];
int i, x, pz, y, X, Y, d[DIM2],p, u, viz[DIM2], c[DIM2], N, M;
int z;
 
void cit(int &x)   
 {   
  x=0;   
  while(vec[pz]<'0' || vec[pz]>'9')   
   
    if(++pz==DIM) fread(vec,1,DIM,stdin),pz=0;   
   
    while(vec[pz]>='0' && vec[pz]<='9')   
    {   
        x=x*10+vec[pz]-'0';   
        if(++pz==DIM) fread(vec, 1, DIM, stdin),pz=0;   
    }   
 }   
int main()
{
    freopen ("sate.in","r",stdin);
    freopen ("sate.out","w",stdout);
    read();
    bfs();
     
    return 0;
}
void read()
{
    cit(N);cit(M);cit(X);cit(Y);
    for (i=1; i<=M; i++)
    {
        cit(x);cit(y);cit(z);
        G[x].push_back(y);
        G[y].push_back(x);
        Cost[x].push_back(z);
        Cost[y].push_back(z);
    }
}
void bfs()
{
    viz[X]=1;
    p=u=0;
    c[p]=X;
    while ( p<=u && !viz[Y])
    {
        x=c[p++];
        for (i=0; i<G[x].size(); i++)
        {
            if (!viz[G[x][i]])
            {   
                if (G[x][i] < x)
                d[G[x][i]]+=(d[x]-Cost[x][i]);
                else d[G[x][i]]+=d[x]+Cost[x][i];
                viz[G[x][i]]=1;
                c[++u]=G[x][i];
            }
        }
    }
printf ("%d\n",d[Y]);
}