#include <iostream>
#include <fstream>
#include <vector>
#define NMax 30005
#define MMax 100030
#define Nod first
#define Value second
using namespace std;
ifstream g("sate.in");
ofstream f("sate.out");
int cost[MMax],uz[NMax],N,M,x,y,z,p1,p2;
vector <pair <int,int> > V[NMax];

void Citire()
{
    g>>N>>M;
    g>>p1>>p2;
    for(int i=1;i<=M;i++)
    {
        g>>x>>y>>z;
        V[x].push_back(make_pair(y,z));
        V[y].push_back(make_pair(x,-z));
    }
}

void DFS(int x)
{
    uz[x]=1;
    for(int i=0;i<V[x].size();i++)
    {
        if(uz[V[x][i].Nod]==0)
        {
            cost[V[x][i].Nod]=cost[x]+V[x][i].Value;
            DFS(V[x][i].Nod);
            if(V[x][i].Nod==y)
                return;
        }
    }
}

int main()
{
    Citire();
    DFS(p1);
    f<<cost[p2];
}