#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("sate.in");
ofstream fout("sate.out");
struct sat
{
    int p1,p2,d,viz;
};
int n,m,x,y,dist;
sat s[30005];

int main()
{
    int i,j,a,ok=0;
    fin>>n>>m;
    fin>>x>>y;
    for(i=1;i<=m;i++)
    {
        fin>>s[i].p1>>s[i].p2>>s[i].d;
        s[i].viz=0;
    }
    a=x;
    for(i=1;i<=m && a<=y;i++)
    {
        for(j=1;j<=m && ok==0;j++)
            if(s[j].viz==0 && (s[j].p1==a || s[j].p2==a))
            {
                if(s[j].p1==a)
                {
                    dist=dist+s[j].d;
                    a=s[j].p2;
                    s[j].viz=1;
                    ok=1;
                }
                else
                    if(s[j].p2==a)
                    {
                        dist=dist-s[j].d;
                        a=s[j].p1;
                        s[j].viz=1;
                        ok=1;
                    }
            }
        ok=0;
    }
    fout<<dist;
    return 0;
}