#include <fstream>
#define N 30002
#include <vector>
#include <deque>
#define INF 2000000000

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

struct bla
{
    int ve,co;
};
vector <bla> graph[N];
bool viz[N];
int dist[N];
deque <int> q;

int main()
{
    int n,m,x,y,X,Y,c,nod;
    f>>n>>m>>X>>Y;
    for(int i=1;i<=m;++i)
    {
        f>>x>>y>>c;
        graph[x].push_back({y,c});
        graph[y].push_back({x,-c});
    }
    for(int i=1;i<=n;++i) dist[i]=INF;
    q.push_back(X);
    dist[X]=0;
    while(!q.empty())
    {
        nod=q.front();
        q.pop_front();
        if(!viz[nod])
        {
            for(int j=0;j<graph[nod].size();++j)
            {
                int vee=graph[nod][j].ve;
                int cost=dist[nod]+graph[nod][j].co;
                if(!viz[vee])
                {
                     dist[vee]=cost;///se stie ca distanta finala dinstre X si Y e unica
                     q.push_back(vee);
                }
            }
            viz[nod]=1;
        }
    }
    g<<dist[Y]<<'\n';
    f.close();
    g.close();
    return 0;
}