#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
using namespace std;
ifstream in ("sate.in");
ofstream out("sate.out");
struct pct{int nod,distanta;};
int const N=30005;
vector <pct> a[N];
int n,m,x,y,dx[N];
queue <int> q;
bool marcat[N];
void citireg()
{
    int x,y,d;  pct aux;
    for(int i=1;i<=m;i++)
    {
        in>>x>>y>>d;
        aux.nod=y;  aux.distanta=d;
        a[x].push_back(aux);
        aux.nod=x;  aux.distanta=d;
        a[y].push_back(aux);
    }
}
int distanta(int x, pct y)
{
    if(x<y.nod) return dx[x]+y.distanta;
    return dx[x]-y.distanta;
}
void bfs(int x)
{
    q.push(x);
    marcat[x]=true;
    while(!q.empty())
    {
        x=q.front();
        q.pop();
        for(int i=0;i<a[x].size();i++)
        {
            pct y=a[x][i];
            if(!marcat[y.nod])
            {
                marcat[y.nod]=true;
                if((dx[y.nod]==0)||(dx[y.nod]>distanta(x,y)))
                {dx[y.nod]=distanta(x,y);   q.push(y.nod);}
            }
        }
    }
}
int main()
{
    in>>n>>m>>x>>y;
    citireg();
    bfs(x);
    out<<dx[y]<<"\n";
    return 0;
}