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

using namespace std;

#define Nmax 30010
vector <pair<int,int> >ad[Nmax] ;
queue <int> q ;
bool b[Nmax] ;
int T[Nmax] , n , m , x , y , d , e , f;

void bfs ( int start , int sf )
{
    q.push(start) ;
    b[start] = true ;
    T[start] = 0 ;
    while ( !q.empty() )
    {
        //if ( T[sf] > 0 ) return ;
        int nod = q.front();
        q.pop();
        b[nod] = true ;
        for ( int i = 0 ; i < ad[nod].size() ; ++i )
        {
            if ( !b[ad[nod][i].first] )
            {

                T[ad[nod][i].first] = T[nod] + ad[nod][i].second ;
                q.push(ad[nod][i].first);
                b[ad[nod][i].first] = true ;
            }
        }
    }
}

int main()
{
    freopen("sate.in","r",stdin);
    freopen("sate.out","w",stdout);

    scanf("%d %d %d %d",&n,&m,&x,&y);
    for ( int i = 1 ; i <= m ; i++ )
    {
        scanf("%d %d %d",&d,&e,&f);
        ad[d].push_back(make_pair(e,f));
        ad[e].push_back(make_pair(d,-f));
    }
    bfs(x,y) ;
    printf("%d ",T[y]);
}