#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];
long dist[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(dist[graf[a][y].first]==INF)
            {
                if(graf[a][y].first<a)
                    dist[graf[a][y].first]=dist[a]-graf[a][y].second;
                else
                    dist[graf[a][y].first]=dist[a]+graf[a][y].second;
                q.push(graf[a][y].first);
            }
        }
    }
}
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];
}