#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 BFS()
{
    q.push({X,0});
    viz[X]=1;

    pair<int,int> nod;
    int dist;

    while(1)
    {
        nod=q.front();
        q.pop();

        for(auto i:L[nod.first])
            if(!viz[i.first])
            {
                viz[i.first]=1;
                if(i.first>nod.first)dist=nod.second+i.second;
                else dist=nod.second-i.second;

                if(i.first==Y)
                {
                    fout<<dist<<"\n";
                    return ;
                }

                q.push({i.first,dist});
            }
    }
}

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});
    }

    BFS();

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