#include <fstream>
#include <vector>

using namespace std;

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

vector <pair <int,int> >l[30005];

int n,m,a,b,i,x,y,d,st,dr,nod,vec,cost,c[30005],drum[30005];
bool v[30005];

int main()
{
    fin >> n >> m >> a >> b;
    for (i=1;i<=m;i++)
    {
        fin >> x >> y >> d;
        l[x].push_back(make_pair(y,d));
        d*=-1;
        l[y].push_back(make_pair(x,d));
    }
    st=dr=1;
    c[1]=a;
    v[a]=1;
    while (st<=dr)
    {
        nod=c[st];
        for (i=0;i<l[nod].size();i++)
        {
            vec=l[nod][i].first;
            cost=l[nod][i].second;
            if (v[vec]==0)
            {
                v[vec]=1;
                drum[vec]=drum[nod]+cost;
                if (vec==b)
                {
                    fout << drum[vec];
                    return 0;
                }
                dr++;
                c[dr]=vec;
            }
        }
        st++;
    }

    return 0;
}