#include <cstdio>
#include <vector>
#include <string>

using namespace std;

#define DIM2 1<<15
#define DIM 8192
void read();
void bfs();
vector <int>G[DIM2];
vector <int>Cost[DIM2];
int 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]);
}