#include <fstream>
#include <vector>
#include <queue>
#include <string.h>


using namespace std;

fstream f("sate.in",ios::in);
fstream g("sate.out",ios::out);

const int nmax=30005,INF=0x3f3f3f3f;

vector < pair <int,int> > a[nmax];

int n,m,x,y,x1,y11,c,aux,i;

void citire()
{
    f>>n>>m>>x>>y;
    if(x>y)
    {
        aux=x;
        x=y;
        y=aux;
    }
    for(i=1;i<=m;i++)
    {
        f>>x1>>y11>>c;
        a[x1].push_back(make_pair(y11,c));
        a[y11].push_back(make_pair(x1,c));
    }
}

void rezolvare()
{
    long long dist[nmax];
    int viz[nmax],nc;
    queue <int> q;
    memset(dist,INF,sizeof(dist));
    memset(viz,0,sizeof(viz));
    q.push(x);
    dist[x]=0;
    nc=x;
    viz[x]=1;
    while (!q.empty())
    {
        nc=q.front();
        q.pop();
        for (vector <pair <int,int> >::iterator it=a[nc].begin();it!=a[nc].end();++it)
            if (!viz[it->first])
            {
                if (nc<it->first) dist[it->first]=dist[nc]+it->second;
                            else dist[it->first]=dist[nc]-it->second;
                viz[it->first]=1;
                q.push(it->first);
            }
    }
    g<<dist[y];
}

int main()
{
    citire();
    rezolvare();
    f.close();g.close();
    return 0;
}