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

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

vector < pair < int, long long > >a[30001];

int n,m,x,y,i,j,vz[30001],d,sol;

void DFS(int nod,int dist)
{
    if(nod==y)
    {
        sol=dist;
        return ;
    }
    else
    {
        for(int k=0;k<a[nod].size();k++)
        {
            int nc=a[nod][k].first;
            if(vz[nc]==0)
            {
                vz[nc]=1;
                if(nc>nod)
                {
                    DFS(nc,dist+a[nod][k].second);
                }
                else
                {
                    DFS(nc,dist-a[nod][k].second);
                }
            }
        }
    }
}

int main()
{
    f>>n>>m>>x>>y;
    for(; m; m--)
    {
        f>>i>>j>>d;
        a[i].push_back(make_pair(j,d));
        a[j].push_back(make_pair(i,d));
    }
    vz[x]=1;
    DFS(x,0);
    g<<sol;
    return 0;
}