#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#define INF 0x3f3f3f3f
using namespace std;

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

vector<pair<int,int> >graf[30001];
int dist[30001];
bool ap[30001];
queue<int> q;
int n,m,x,Y;

void bfs(int k)
{
    q.push(k);
    dist[k]=0;
    while(!q.empty())
    {
        int a=q.front();
        q.pop();
        for(int y=0;y<graf[a].size();y++)
        {
            if(!ap[graf[a][y].first])//dist[graf[a][y].first]==INF)
            {
                if(graf[a][y].first<a)
                    dist[graf[a][y].first]=dist[a]-graf[a][y].second;
                else if(graf[a][y].first>a)
                    dist[graf[a][y].first]=dist[a]+graf[a][y].second;
                if (graf[a][y].first==Y)
                {
                    return;
                }
                q.push(graf[a][y].first);
                ap[graf[a][y].first]=1;
            }
        }
    }
}
int main()
{
    int i,a,b,c;
    in>>n>>m>>x>>Y;
    for(i=1;i<=n;i++)
    {
        in>>a>>b>>c;
        graf[a].push_back(make_pair(b,c));
        graf[b].push_back(make_pair(a,c));
    }
    for(i=0;i<=n;i++)
        dist[i]=INF;
    bfs(x);
    out<<dist[Y];
}