#include<fstream>
#include<queue>
#include<vector>
using namespace std;

ifstream in("sate.in");
ofstream out("sate.out");

struct segment{
    int fin,dist;
};

int X,Y,n,m,rez,sate[30001];
vector <segment> v[30001];
queue <int> q;


segment makestruct(int x,int y)
{
    segment a;
    a.fin=x;a.dist=y;
    return a;
}


void bfs()
{
    int x,y;
    while(!q.empty())
    {
        int curent=q.front();
        q.pop();
        if(curent==Y)
        {
            rez=sate[curent];
            return;
        }
        for(int i=0;i<v[curent].size();i++)
        {
            x=curent;
            y=v[curent][i].fin;
            if(x<y)
            {
                q.push(y);
                sate[y]=sate[curent]+v[curent][i].dist;
            }
            else{
                q.push(y);
                sate[y]=sate[curent]-v[curent][i].dist;
            }
        }
    }
}
int main()
{
    int i,x,y,dist;
    in>>n>>m>>X>>Y;

    for(i=1;i<=m;i++)
    {
        in>>x>>y>>dist;
        v[x].push_back(makestruct(y,dist));
        v[y].push_back(makestruct(x,dist));
    }

    for(i=0;i<v[X].size();i++)
    {
        q.push(v[X][i].fin);
        sate[v[X][i].fin]=v[X][i].dist;
    }

    bfs();
    out<<rez;
}