#include <bits/stdc++.h>

using namespace std;

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

const int Nmax=3e4+2;

int n,m,X,Y;
bitset<Nmax>viz;
vector<pair<int,int> >L[Nmax];
queue<pair<int,int> >q;

void Dfs(int nod,int dist)
{
    viz[nod]=1;
    for(auto i:L[nod])
    {
        if(i.first==Y)
        {
            fout<<dist+i.second<<"\n";
            exit(0);
        }

        if(!viz[i.first])Dfs(i.first,dist+i.second);
    }
}

int main()
{
    fin>>n>>m>>X>>Y;

    int x,y,d;
    for(int i=1;i<=m;i++)
    {
        fin>>x>>y>>d;
        L[x].push_back({y,d});
        L[y].push_back({x,-d});
    }

    Dfs(X,0);

    fin.close();
    fout.close();
    return 0;
}