#include <cstdio>
#include <vector>
#include <queue>

using namespace std;

#define lim 30010
int n,m,x,y,a,b,c;
struct loc{int sat,d;};
bool viz[lim];
vector <loc> G[lim];
int dist[lim];


void bfs(int nod)
{
    queue <int> q;
    q.push(nod);
    dist[nod]=0;

    while(!q.empty())
    {
        nod=q.front();
        q.pop();
        for(auto it:G[nod])
        {
            if(!viz[it.sat])
            {
                viz[it.sat]=true;
                if(it.sat>nod)
                {
                    dist[it.sat]=dist[nod]+it.d;
                    q.push(it.sat);
                }
                if(it.sat<nod)
                {
                    dist[it.sat]=dist[nod]-it.d;
                    q.push(it.sat);
                }
            }
        }
    }

}


int main()
{
    FILE *fin, *fout;
    fin = fopen("sate.in","r");
    fout = fopen("sate.out","w");
    fscanf(fin,"%d%d%d%d",&n,&m,&x,&y);

    for(int i=1; i<=m; i++)
    {
        fscanf(fin,"%d%d%d",&a,&b,&c);
        G[a].push_back({b,c});
        G[b].push_back({a,c});
    }
    fclose(fin);


    bfs(x);
    fprintf(fout,"%d\n",dist[y]);
    fclose(fout);

    return 0;
}